Kentucky Extension Master Gardener Program Manual PDF

The Kentucky Extension Master Gardener Program The Kentucky Extension Master Gardener Program manual (ID-1) is also available as an online publication. The digital version, including links to additional resources referenced throughout this publication, can be accessed at http://www2.ca.uky.edu/agc...

The Kentucky Extension Master Gardener Program The Kentucky Extension Master Gardener Program manual (ID-1) is also available as an online publication. The digital version, including links to additional resources referenced throughout this publication, can be accessed at http://www2.ca.uky.edu/agcomm/pubs/id/id1/id1.pdf  The Kentucky Extension Master Gardener Program Publication Chapter Title Page Number Intro The Kentucky Extension Master Gardener Program i 1 Basic Botany 1 HO-96 2 Plant Identification 23 HO-97 3 Plant Propagation 27 HO-98 4 Soils and Fertility 39 AGR-204 5 Plant Diseases 57 PPA-46 6 Diagnosing Plant Problems 77 ID-194 7 Insects 101 ENT-68 8 Weed Management 117 AGR-205 9 Vertebrate Pest Management 127 FOR-121 10 Integrated Pest Management 135 ENT-69 11 Pesticides and Pesticide Safety 143 ENT-70 12 Your Yard and Water Quality 151 ID-201 13 Composting 157 ID-192 14 Landscape Design 163 HO-105 15 Lawn Management 179 AGR-206 16 Selecting and Planting Woody Plants 195 HO-107 17 Care of Woody Plants 209 HO-101 18 Annual and Perennial Flowers 223 HO-102 19 Indoor Plants 233 HO-103 20 Home Vegetable Gardening in Kentucky 243 ID-128 21 Organic Gardening 299 HO-100 22 Growing Tree Fruits 307 HO-104 Index Index 317 Introduction The Kentucky Extension Master Gardener Program Edited by Richard Durham, consumer horticulture Extension specialist and state Master Gardener coordinator, and Sharon Bale, Extension floriculture specialist (ret.), University of Kentucky. the liberal and practical education of the industrial classes in In this chapter: the several pursuits and profession in life.” After the Civil War, this land-grant opportunity was The Start of Extension i extended to the former Confederate states and to states created How Does the System Work? ii after 1862. If a state did not have enough federal land to meet the requirement for funding, the state was issued “script,” which Idea Sources for Programs iii meant that the state could select federal lands in other states to Current Conditions iii create funding for these schools. The Morrill Act of 1862 authorized “separate but equal” What Can You Do for the Cooperative Extension Service? iv facilities for African-Americans. Mississippi and Kentucky were The Extension Master Gardener Program iv the only two states to provide this type of education. The pro- Expectations for Extension Master Gardener Volunteers vi posed second Morrill Act was aimed at the former Confederate states. It required each state to show proof that race was not a requirement for admission or to create a separate land-grant I n the mid-19th century, there was a political movement call- institution that would admit African-Americans. This bill was ing for the creation of agriculture colleges. The movement passed in 1890. Although cash was granted for these institu- was led by Jonathan Turner, a professor at Illinois College. tions instead of land, they have the same legal standing as the In 1853, the Illinois Legislature adopted a resolution calling 1862 land-grant schools. Sixteen African-American land-grant for the Illinois congressional delegation to work toward enact- colleges were established throughout the South and are known ing a bill that would create the land-grant system. They thought as 1890 land-grant institutions. In Kentucky, the University of a congressman from the eastern part of the country would have Kentucky is the 1862 land-grant school and Kentucky State better luck getting this type of legislation through Congress, so University is the 1890 land-grant school. Rep. Justin Smith Morrill of Vermont was recruited to intro- Congress soon realized that to be effective, the educational duce the bill. function of land-grant universities must be supplemented with Unlike the original proposal, the Morrill bill allocated land research capability. Consequently, it passed the Hatch Act in based on the number of senators and representatives each 1887. This act provided for the establishment of facilities where state had in Congress. Under the act each eligible state would colleges could conduct research into agricultural, mechanical, receive 30,000 acres of federal land—either within or contigu- and related problems faced by rural citizenry. Congress also saw ous to its boundaries—for each member of Congress the state a need to disseminate the knowledge gained at the land-grant had according to the census of 1860. The land was to provide colleges to the general public, farmers and homemakers being a financial base for the funding of these schools. the initial focus. The original bill passed in 1859, but was vetoed by President James Buchanan. In 1861, the bill was resubmitted with an The Start of Extension amendment that included military tactics as well as engineering and agriculture. Many of the Southern states did not support Extension had its beginnings in the movement to improve this type of legislation, but because they began to secede from agricultural production. Seaman Knapp’s successful use of the the United States, the bill was passed and signed into law by demonstration method on Louisiana farms in the fight against President Abraham Lincoln in July of 1862. The Southern states the cotton boll weevil served as the model for legislation. The that seceded were not given access to the federal land. Cooperative Extension Service was created by the federal The purpose of the land-grant colleges was, “without exclud- government in 1914 by the passage of the Smith-Lever Act. ing other scientific and classical studies and including military Section 2 of that Act, which was in effect as of June 23, 1972 tactic, to teach such branches of learning as are related to agri- (U.S.C. 341 et seq.), says: culture and the mechanic arts, in such manner as the legislatures “Cooperative Agricultural Extension work shall consist of the of the States may respectively prescribe, in order to promote giving of instruction and practical demonstrations in agriculture and home economics and subjects relating thereto to persons not i INTRODUCTION The Kentucky Extension Master Gardener Program attending or resident in said colleges in the several communities, Federal and imparting information on said subjects through demonstra- tions, publications, and otherwise and for the necessary printing United States Department of Agriculture and distribution of information in connection with the foregoing, Secretary of Agriculture and this work shall be carried on in such manner as may be At the federal level, agencies support Cooperative Extension mutually agreed upon by the Secretary of Agriculture and the through research grants and cooperate in setting policy and State agricultural college or colleges or Territory or possession focusing issues to guide its mission. receiving the benefits of this Act.” The 1940s and 1950s began a period of rapid technological State advancement in American agriculture. Farmers improved Land-Grant Institutions their competitive position primarily through the adoption of improved management practices, the expansion of their University of Kentucky—University supervises the Extension resource base, and increased efficiency. This led to production program throughout the state. surpluses and a heavy reliance upon agricultural production in 1890 Institutions international trade and development assistance. With an abun- Kentucky State University—Extension efforts are focused on the dance of reasonably priced food supply pretty much assured, urban environment and small farms. national attention, and to some extent the concern of Extension, in the 1960s shifted to the problems of urban, low-income, and State Extension Specialists minority residents. Extension specialists exist from most academic disciplines, At the same time, there was a substantial reduction in the including agricultural economics, communications, biosystems size of the farm and rural population. In 1910, approximately and agricultural engineering, plant and soil sciences, animal and 35 percent of the U.S. population were classified as farmers, and food sciences, entomology, forestry, 4-H youth development, until 1940, almost one-quarter of the population were farmers. human environmental sciences, horticulture, plant pathology, Since that time, the farm population has declined to less than community and leadership development, and rural and eco- three percent of the population. A similar decline occurred in nomic development. Within the Department of Horticulture, the rural portion of the population. At the turn of the century, there are state specialists or Extension associates for youth more than 50 percent of the nation’s population lived in a loca- programming, consumer horticulture, woody plants, fruits, tion defined as rural. In 1980, less than 30 percent did. As these greenhouse crops, vegetables, annuals, and perennial flowers. rural and farm residents relocated in metropolitan centers, they Specialists take research information and provide it to county carried with them an awareness of what Extension did for them agents, growers, consumers, youth, policy makers, and other in rural areas, setting the stage for an urban clientele. clients. The Cooperative Extension Service takes information gen- erated by research scientists and presents it to the public in layman’s terms. This concept is called technology transfer and Local it is what Cooperative Extension is all about—providing up-to- County Agents date, unbiased, scientifically based information to the public in The county staff (usually agriculture and natural resources, a manner they can understand. family and consumer sciences, 4-H youth development agents, and in some cases, horticulture agents with support staff ) How does the system work? develop their own programs and, when necessary, rely on state specialists to provide them with specific content information The Cooperative Extension Service is a partnership between for their educational programming needs. A local Extension the United States Department of Agriculture (USDA), State council is formed for each county. These councils are made up Cooperative Extension Services, land-grant universities, 1890 of local citizens who determine program priorities. They then institutions and county government. Funding for Cooperative support the county staff in their efforts to deliver relevant, Extension Service is provided by federal, state, and local gov- high-quality programs to people of the county. ernments. Policy considerations, program development and program emphasis are developed through cooperative efforts. Volunteers In fact, the Extension Service is very much a grass-roots orga- For strategic planning to be successful and for there to be nization, often focused on local issues. a unified approach to societal concerns or issues, volunteers The components of Cooperative Extension include organiza- serving on planning and advisory councils help to focus pro- tions and personnel at the federal, state and local levels. gramming on the needs of traditional and new clients and concentrate resources in a few areas of major concern. When there is adequate volunteer commitment and support, large numbers of impactful programs can be supported by a small ii  The Kentucky Extension Master Gardener Program INTRODUCTION team of Extension agents. This is where volunteers such as In many states, during the 1950s and 1960s emphasis was Extension Master Gardeners can serve a critical role in extend- placed on each county Extension Service developing an indi- ing Extension programming to a wider audience. vidual county plan—in consultation with local people—based on identifying the greatest needs. Program Planning State plans of work often were a composite of individual The Secretary of Agriculture has delegated responsibility for county plans. Campus departments assisted counties by pro- program planning to the Extension staff within the Department viding information to Extension agents and leaders about areas of Agriculture. General boundaries of programs that were where they saw developing needs. USDA held annual Outlook expected over the past 20 years have been periodically defined Conferences that briefed state staff on emerging problems by “scope” reports developed by a committee established by and economic changes. But the county plan was sacrosanct the USDA Extension administrator and directors of Extension. in many states. Each county, in consultation with local people, Such reports usually are published every 10 years or so. They established what Extension agents in that county would focus provide historical evidence of how policy changes relate to what upon for the next year. is appropriate for federal funding under the Smith-Lever Act. Community development became an important fourth The law also requires that “before the funds herein provided program area with Extension Services in Kentucky and several shall become available to any college for any fiscal year, plans other states, adding county positions or encouraging other for the work to be carried on under this Act shall be submit- agents to increase programming in such areas. ted by the proper officials of each college and approved by the Because needs among clientele differ, Extension programs Secretary of Agriculture.” at the local level have become more diverse. In Kentucky, proj- Each state must provide one statewide plan with various ects available to 4-H members went from about 20 projects specific research and program directives, and those plans must focused on farming and homemaking to more than 250 that be agreed to by the USDA Extension Service before a state can included any area that would help a young person learn and receive federal funding. develop life skills. With the help of media and volunteers, county Extension agents and state Extension specialists stretched their resources Idea Sources for Programs to cover a multitude of subjects each year. Although several Three main sources of Extension programs have emerged. states encouraged agents to focus on at least one intensive Research/academic disciplines—The campus department and project that concentrated resources on a specific area for the USDA research branch were historically a main source of several months, most agents preferred to take the cumulative what would be emphasized in the Extension programs. Early route. They found themselves acting as generalists, responding specialists were guided by what departments viewed as impor- to a host of local questions and needs. They preferred to cover tant information for farm families. In the 1930s and 1940s, all areas a little bit each year with the expectation that over for example, there was considerable concentration across the a five- or six-year period substantial practice changes would United States in introducing farmers to hybrid seed corn and occur in all areas. in improved seed/cuttings for other crops that were developed Societal Needs—Societal needs have always been present as one through Experiment Station Research. source of programming but have not always been recognized The first state plans of work were primarily developed within as a dominant influence. Research often has been stimulated departments based upon the best judgment of the research, by major social problems, such as scarcity of food or the need resident, and instruction faculty as to what areas should be to conserve soil. Grass-roots planning often yielded programs emphasized. that not only met individual needs of clients but were directed Researchers and administrators at land-grant universi- toward common needs that were held by a larger group. Many ties and the USDA have continued to view disseminating counties were fortunate enough to have wise leaders who could research findings and encouraging their use as a main role of influence others on planning committees to see beyond their the Extension system. own immediate needs and to encourage programs like land-use Grass-roots planning—However, as the Extension service planning and zoning. moved to county locations, leaders became much more aware Thus, over the years, Extension programs carried on in any of the vast differences among counties across the country and county or state have been influenced to different degrees by even within a given state. The people in some counties were research, individual client needs, and the needs of society. much farther ahead in relation to knowing and following rec- ommended practices. Some were much farther behind. Before the advent of television, communities and counties were fairly Current Conditions isolated. As the academic field of adult education developed Two major factors affect the nature of Extension programs in the 1940s and 1950s, one of the cardinal principles was that and the way those programs are decided. education was much more likely to be successful if programs Rural families not only make up a smaller percentage of the were based upon needs. U.S. population, but because a greater share of the nation’s iii INTRODUCTION The Kentucky Extension Master Gardener Program food supply comes from other countries, the broader Consequently, the Extension Master Gardener Program was population is no longer dependent upon the American created in 1973 in the state of Washington. Since then it has farmer. Rather than dominating American society, as was spread nationwide. Master Gardeners have become a vital part the case when Extension was started in 1914, farmers and of Extension’s ability to provide consumers with up-to-date, rural communities have become a small minority struggling reliable knowledge so they can enjoy and protect the plantings to maintain programs established by Congress and state around their homes. Master Gardening also has become a fun legislatures. and useful volunteer activity that has given its participants a The pool of tax dollars has diminished at national, state, sense of community spirit, accomplishment, and intellectual and local levels; and competition for those dollars is vastly stimulation. increased. Today, nearly 100,000 Extension Master Gardener volun- There is continuing pressure on Extension to: teers are active in all 50 states and the District of Columbia. Show that its programs are important to American society These programs seek to engage diverse audiences both as as a whole and benefit people beyond its direct clientele volunteers and through outreach efforts. Local agents, advi- Show substantial impact from money invested sory councils and volunteer leaders are committed to offering Show substantial efforts on major problem areas nationwide programs that serve all people regardless of race, color, age, sex, For example, water purity is of keen importance to all religion, disability, or national origin. Americans. Our health and safety from major illness and disease depend upon the quality of water. The agricultural Your Responsibility as an industry (farming, processing, and packaging) is one source of Extension Master Gardener pollutants. Because of Extension’s direct focus on farming, the Cooperative Extension Service puts considerable emphasis When you enter the Extension Master Gardener Program, on those practices that increase the purity of water. Extension you are entering into a contract. In essence, you agree that in administrators are encouraging counties and states to concen- return for the training you receive, you will volunteer a prede- trate some of their programming resources on water quality termined number of hours back to Extension. Failure to com- and other areas that are of major concern to society in general. plete this obligation means you are not entitled to wear a Master Cooperative Extension is constantly challenged to be a Gardener badge, nor participate in Master Gardener activities. dynamic educational organization. This challenge forces Upon completion of your training, you have one year to Extension to be contemporary, progressive, and visionary. complete the agreed-upon volunteer service commitment, also called payback time. This time requirement varies from one Extension unit to another. What Can You Do for the Cooperative After you complete your payback time, you may choose Extension Service? to continue with the Extension Master Gardener Program. Numerous people have worked as Master Gardeners for years Volunteer workers are one of the most important and unique and contributed substantial amounts of time to Extension. To aspects of the Cooperative Extension Service. This is in keeping be considered an active Master Gardener, however, you must with Extension’s philosophy that active citizen participation agree to volunteer a minimum number of hours annually. In in planning and implementation insures program success. Kentucky the current requirement for new trainees is 40 hours As an Extension Master Gardener, you will join this family of of volunteer service to obtain their initial certification as a volunteers. Master Gardener. To renew certification, Master Gardener volunteers must complete 20 hours of volunteer service and 10 hours of continuing education credit each year. The county The Extension Master Gardener Program agent in charge of the local program determines what activi- The Extension Master Gardener Program was created to ties count toward volunteer service and continuing education meet an increase in requests from home gardeners for hor- credits. ticultural information. This increase derives primarily from Report Volunteer Time—Time sheets were historically used the urban and transient nature of modern American life. Fifty to keep track of the hours of time you volunteer as a Master years ago, an Extension agent dealt with the questions of a few Gardener and some programs continue to use this method. hundred farm families. In many regions, however, land that Some programs may appoint a Master Gardener to keep track once constituted a single farm now encompasses several sub- of this information. Other programs use on-line methods of divisions, increasing the number of families an Extension office reporting volunteer hours. Whatever the method of reporting must serve. In addition, many of these families are unfamiliar your time, don’t be lax; the reported hours are used in county with the grasses, shrubs, trees, and diseases that comprise the progress reports, and you deserve recognition for your efforts. microenvironment of their new home. They often will call their Use of the Title “Extension Master Gardener”—The title “Extension local Extension office for advice on what to plant and how to Master Gardener” should be used only by individuals trained care for it. in a Cooperative Extension Service program. The title is valid iv  The Kentucky Extension Master Gardener Program INTRODUCTION only when used by an active Extension Master Gardener who additional training hours and subject matter will be determined is participating in a program approved by an Extension agent. by the agent’s program and need for volunteer assistance. When an individual ceases to be active in the Extension Master Upon completion of the training program, a candidate must Gardener program, their designation as an Extension Master pass a written final examination before they can be designated a Gardener ceases. Master Gardener. The final exam will consist of 100 total points Extension Master Gardeners should not display credentials possible. Seventy-five percent of the possible points will come or give the appearance of being an Extension Master Gardener from questions on material covered in the core curriculum. The at a place of business unless that place is designated by the remaining 25 percent of the points will come from questions county office as a place where an Extension educational pro- developed by the county agent and based on material covered gram is taking place. The title “Extension Master Gardener” in the additional training. should not be used in a manner which implies Cooperative After the candidate has passed the written exam, they will Extension Service endorsement of any product or place of receive a Kentucky Extension Master Gardener certificate business. and a Master Gardener name badge. They also will be asked to The title “Extension Master Gardener” should be used only choose which volunteer activities they would like to perform when doing unpaid volunteer work for Extension. When in order to fulfill their commitment to the Master Gardener experienced Extension Master Gardeners speak before groups program. Volunteer activities often include unsupervised work on horticultural subjects, they may accept unsolicited reim- with vulnerable audiences, and background checks are required bursements (such as reimbursements for expenses) or gifts. It prior to commencing training. is inappropriate, however, to seek speaking engagements for pay while participating in an authorized Extension activity and using the title “Extension Master Gardener.” Transfer of Certification from Other States A Word of Caution—When you work as an Extension Master Master Gardener certification from other states will be Gardener, you are acting as a representative of the Cooperative honored at the discretion of the county agent in charge of the Extension Service. While Master Gardeners are covered by program. The agent may accept the transfer of certification Extension’s liability insurance when performing their volunteer outright or may require the Master Gardener to participate duties in regard to sharing horticultural information, the Master in one or more of the Master Gardener training sessions that Gardener needs to be concerned that any information given to may contain information of a state-specific nature. Kentucky the general public should be factual and based on Cooperative certification will be granted once the Master Gardener has Extension recommendations. Do not be afraid to say, “I do not completed any needed training and performed 20 hours of know the answer to that question.” volunteer service. One particular area of concern is pesticide recommen- dations. Master Gardeners know that the use of chemicals What Does a Master Gardener Do? in the garden is usually a last resort. Under the amended Federal Insecticide, Fungicide, and Rodenticide Act (Federal The local Extension agent will supply the Master Gardeners Environmental Control Act of 1972), it is illegal to use a pesti- with a list of volunteer job descriptions (see the Sample Job cide on a crop unless the crop is listed on the label. The given Description). These jobs will be focused on the needs of that rate of application on the label may not be exceeded. Fines and particular agent as well as the needs of the county. No volun- other penalties vary according to the laws broken. Please refer teer will be asked to participate in an activity they do not feel all pesticide questions to the county agent unless you have been comfortable doing or are not physically able to do. The variety specifically told by the county agent that a certain recommen- of jobs available should enable any volunteer to find an area in dation can be made. which to perform their payback time. Master Gardener Curriculum Table 1. Master Gardener Training The focus of local Extension programs can be diverse. As Core Subjects Number of Hours Training Required such, the Extension Master Gardener training program must Cooperative Extension/ maintain some flexibility and allow the county agent to deter- 2 hours Volunteerism mine where emphasis should be placed. Although flexibility Botany 6 hours with lab is desirable, it has been determined that all Master Gardener candidates must complete a minimum of training in certain Soils and Fertility 4 hours with lab core subjects (Table 1). Plant Pathology 4 hours with lab In addition to the core requirement material, the agent will Entomology 4 hours with lab require additional hours of training to address specific subjects Pesticides/Pesticide Safety/ such as propagation, woody plant material, or vegetables. The 4 hours Environmental Issues Total 24 core hours of training v INTRODUCTION The Kentucky Extension Master Gardener Program The primary purpose of these expectations for volunteers is Sample Job Description* to ensure the safety and well-being of all participants. Kentucky Job Title: Senior Citizen Community Garden Cooperative Extension Service volunteers are expected to Volunteers Needed: Two function within the guidelines of the Kentucky Cooperative Extension Service and its various organizations. Major Objectives: To be event coordinator for the opera- tion of the community garden The following statements relate to the role of a volunteer with the Kentucky Cooperative Extension Service: Responsibilities: Arrange weekly garden work sessions and assist mem- I will represent the Kentucky Cooperative Extension Service bers in running the sessions by conducting myself with courteous manners and language, Help plan garden meetings, programs and events serving as a positive role model, and demonstrating reason- Help procure supplies and plant material for the garden Coordinate the planting and maintenance of the garden able conflict-resolution skills. Generate publicity for garden activities I will abide by all applicable laws and Cooperative Extension Training: Service rules, policies, and guidelines. This includes, but is One two-hour training not limited to, child abuse, fiscal management procedures, Update meetings as necessary and substance abuse. Time Involved: I will accept supervision and support from salaried Extension Day time meetings Approximately 8 hours per month including meetings, staff or designated management volunteers. garden visits and preparation I will make all reasonable efforts to ensure that programs are 64 hours per volunteer accessible to all individuals regardless of race, color, age, sex, Length of Commitment: 8 months religion, disability, or national origin. Program Contact: County Agent I will participate in orientation and training related to the * This job in no way implies employment with the University. Extension Master Gardener Program, sponsored by the Kentucky Cooperative Extension Service. I will not consume or allow others to use alcohol or illegal The Extension agent is responsible for providing a number of drugs while involved in any Kentucky Cooperative Extension job possibilities that can utilize the talents and expertise of the Service-sponsored program. Master Gardener. In recent years, creative Master Gardeners I will, when engaged in Kentucky Cooperative Extension and Extension agents have recognized that talents which citi- Service activities, operate motor vehicles and other equip- zens bring to the Master Gardener program can be utilized in ment in a safe and reliable manner and only with a valid a variety of horticultural activities. Sometimes it just takes a operator’s license. I will comply with all motor vehicle-related suggestion to create a new area of Master Gardener activity. state regulations and laws, including those regulating the Don’t be afraid to make suggestions. proper use of seat belts for adults and youth. I will accept the responsibility to promote and support the vision, mission, and values of the Kentucky Cooperative Can a Volunteer be Fired? Extension Service. Well, maybe reassigned would be a better term. For example, I will conduct myself in a manner that is in the best interest a particular Master Gardener may agree to fill the job as a tour of the Kentucky Cooperative Extension Service and will not guide for a demonstration garden. The tours are supposed to use the volunteer position for purposes of private or personal be conducted at 2:00 p.m. on Tuesdays and Thursdays. The gain. particular Master Gardener turns out to be one of those people I will use technology in an appropriate manner that reflects who always is running 15 minutes behind schedule. It is then the the best practice in volunteer service to the Kentucky Extension agent’s responsibility to discuss the matter with the Cooperative Extension Service. Master Gardener and if necessary reassign the Master Gardener to a job that does not have such time constraints. These expectations represent a contractual agreement between volunteers and the Kentucky Cooperative Extension Expectations for Extension Service. By continuing with the Master Gardener training and becoming a certified Kentucky Extension Master Gardener, Master Gardener Volunteers you agree to adhere to these expectations. Kentucky residents place trust in the Kentucky Cooperative Extension Service to provide quality leadership and reliable, unbiased information. The opportunity to represent the Kentucky Cooperative Extension Service is a privileged posi- tion of trust that should be held only by those who are willing to demonstrate behaviors that fulfill this trust. vi Chapter 01 Basic Botany By Ann Marie VanDerZanden, former Extension Master Gardener state coordinator, Oregon State University. Adapted for Kentucky by Richard Durham, consumer horticulture Extension specialist and state Master Gardener coordinator, University of Kentucky. distinguishing characteristics. For example, monocots (e.g., In this chapter: grasses) produce only one seed leaf, while dicots (broadleaf plants) have two. The vascular systems, flowers, and leaves Plant Life Cycles 01 of the two types of plants also differ (Table 1.1). These differ- ences will be important in our discussion of plant growth and Botany Terminology 02 development. Internal Plant Parts 02 External Plant Parts 02 Plant Life Cycles Stem Terminology 05 Based on its life cycle, a plant is classified as either an annual, Plant Growth and Development 15 biennial, or perennial. Environmental Factors Affecting Growth 16 An annual, such as a zinnia, completes its life cycle in one year. Annuals are said to go from seed to seed in one year or Plants in Communities 20 growing season. During this period, they germinate, grow, Plant Hormones and Growth Regulators 21 mature, bloom, produce seeds, and die. Summer annuals complete their life cycle during spring and summer; most For More Information 22 winter annuals complete their growing season during fall and winter. There are both winter and summer annual weeds, and P understanding a weed’s life cycle is important to controlling it. lants are essential to life on earth. Either directly or indi- A biennial requires all or part of two growing seasons to rectly, they are the primary food source for humans and complete its life cycle. During the first season, it produces veg- other animals. Additionally, they provide fuel, replenish etative structures (leaves) and food storage organs. The plant the earth’s oxygen supply, prevent soil erosion, slow down overwinters and then produces flowers, fruit, and seeds during wind movement, cool the atmosphere, provide wildlife habitat, its second season. Swiss chard, carrots, beets, sweet William, supply medicinal compounds, and beautify our surroundings. and parsley are examples of biennials. Many plants are familiar to us, and we can identify and Sometimes biennials go from seed germination to seed appreciate them based on their external structure. However, production in only one growing season. This situation occurs their internal structure and function often are overlooked. when extreme environmental conditions, such as drought or Understanding how plants grow and develop helps us capitalize temperature variation, cause the plant to pass rapidly through on their usefulness and make them part of our everyday lives. the equivalent of two growing seasons. This phenomenon is This chapter focuses on vascular plants—those that contain referred to as bolting. Sometimes bolting occurs when biennial water-, nutrient-, and food-conducting tissues called “xylem” plant starts are exposed to a cold spell before being planted in and “phloem.” Ferns and seed-producing plants fall into the garden. this category. Perennial plants live more than two years and are grouped In several cases, we will distinguish between monocotyledon- into two categories: herbaceous perennials and woody peren- ous and dicotyledonous plants. Sometimes called “monocots” nials. Herbaceous perennials have soft, nonwoody stems that and “dicots” for short, these plants have several important Table 1.1. Comparison of monocots and dicots. Structure Monocots Dicots Seed leaves (cotyledons) one two Vascular system Xylem and phloem are paired in bundles, Xylem and phloem form rings inside the stem. The phloem forms which are dispersed throughout the stem. an outer ring, the xylem an inner ring. In long-lived woody perenni- als, yearly concentric rings are produced. Floral parts Usually in threes or multiples of three. Usually in multiples of four or five. Leaves Often parallel-veined. Generally net-veined. 1-01 CHAPTER 01 Basic Botany generally die back to the ground each winter. New stems grow from the plant’s crown each spring. Trees and shrubs, on the Botany Terminology Anther—The pollen sac on a male flower. other hand, have woody stems that withstand cold winter tem- peratures. They are referred to as woody perennials. Apex—The tip of a shoot or root. Apical dominance—The tendency of an apical bud to produce hormones that suppress growth of buds below it on the stem. Internal Plant Parts Axil—The location where a leaf joins a stem. Cells are the basic structural and physiological units of plants. Cambium—A layer of growing tissue (meristem) that separates the xylem and phloem and produces new xylem and phloem cells. Most plant reactions (cell division, photosynthesis, respiration, etc.) occur at the cellular level. Plant tissues (meristems, xylem, Chlorophyll—The green pigment in leaves that is responsible for captur- ing light energy from the sun. phloem, etc.) are large, organized groups of similar cells that work together to perform a specific function. Chloroplast—A specialized component (organelle) of certain cells; con- tains chlorophyll and is responsible for photosynthesis. A unique feature of plant cells is that they are readily toti- Cortex—Cells that make up the primary tissue of the root and stem. potent. In other words, almost all plant cells retain all of the genetic information (encoded in DNA) necessary to develop Cotyledon—The first leaf that appears on a seedling. Also called a seed leaf. into a complete plant. This characteristic is the main reason Cuticle—A relatively impermeable surface layer on the epidermis of that vegetative (asexual) reproduction works. E.g., the cells of a leaves and fruits. small leaf cutting from an African violet have all of the genetic Dicot—Having two cotyledons or seed leaves. information necessary to generate a root system, stems, more leaves, and ultimately flowers. Epidermis—The outermost layer of plant cells. Specialized groups of cells called meristems are a plant’s Guard cell—Epidermal cells that open and close to let water, oxygen, and carbon dioxide pass through the stomata. growing points. Meristems are the site of rapid, almost continu- ous cell division. These cells either continue to divide or begin Internode—The space between nodes on a stem. to differentiate into other tissues and organs. How they divide Meristem—Specialized groups of cells that undergo cell division and are a plant’s growing points. and whether they ultimately become a tissue or an organ are controlled by a complex array of internal plant hormones but Mesophyll—A leaf’s inner tissue, located between the upper and lower epidermis; contains the chloroplasts and other specialized cellular also can be influenced by environmental conditions. In many parts (organelles). cases, you can manipulate meristems to make a plant do some- Monocot—Having one cotyledon or seed leaf. thing you want, such as change its growth pattern, flower, alter Node—An area on a stem where a leaf, stem, or flower bud is located. its branching habit, or produce vegetative growth. Ovary—The part of a female flower where eggs are located. Also, the base of the pistil. External Plant Parts Petiole—The stalk that attaches a leaf to a stem. External plant structures such as leaves, stems, roots, flow- Phloem—Photosynthate-conducting tissue. ers, fruits, and seeds are known as plant organs. Each organ is Photosynthate—A food product (sugar or starch) created through photosynthesis. an organized group of tissues that work together to perform a specific function. These structures can be divided into two Photosynthesis—The process in green plants of converting carbon dioxide and water into food (sugars and starches) using energy from groups: sexual (reproductive) and vegetative. Sexual or repro- sunlight. ductive parts produce seed; they include flower buds, flowers, Pistil—The female flower part; consists of a stigma, style, and ovary. fruit, and seeds. Vegetative parts (Figure 1.1) include roots, Respiration—The process of converting sugars and starches into energy. stems, shoot buds, and leaves; they are not directly involved in sexual reproduction. Vegetative parts often are used in asexual Stamen—The male flower part; consists of an anther and a supporting filament. forms of reproduction such as cuttings, budding, or grafting. Stigma—The top of a female flower (pistil) part; collects pollen. Stoma (pl. stomates, stomata)—Tiny openings in the epidermis that allow Roots water, oxygen, and carbon dioxide to pass into and out of a plant. Often roots are overlooked, probably because they are less Style—The part of the female flower (pistil) that connects the stigma visible than the rest of the plant. However, it’s important to to the ovary. Pollen travels down the style to reach the ovary, where fertilization occurs. understand plant root systems because they have a pronounced Transpiration—The process of losing water (in the form of vapor) effect on a plant’s size and vigor, method of propagation, through stomata. adaptation to soil types, and response to cultural practices Turgor—Cellular water pressure; responsible for keeping cells firm. and irrigation. Vascular tissue—Water-, nutrient-, and photosynthate-conducting tissue (xylem and phloem). Xylem—Water- and nutrient-conducting tissue. 1-02  Basic Botany CHAPTER 01 Roots typically originate from the lower portion of a plant The zone of maturation is directly beneath the stem. Here, or cutting. They have a root cap but lack nodes and never bear cells become specific tissues such as epidermis, cortex, or leaves or flowers directly. Their principal functions are to absorb vascular tissue. nutrients and moisture, anchor the plant in the soil, support A root’s epidermis is its outermost layer of cells (Figure 1.3). the stem, and store food. In some plants, they can be used These cells are responsible for absorbing water and minerals for propagation. dissolved in water. Cortex cells are involved in moving water from the epidermis to the vascular tissue (xylem and phloem) Structure and in storing food. Vascular tissue is located in the center of Internally, there are three major parts of a root (Figure 1.2): the root and conducts food and water. The meristematic zone is at the tip and produces new cells; Externally, there are two areas of importance: the root it is an area of cell division and growth. cap and the root hairs (Figure 1.2). The root cap is the root’s Behind the meristem is the zone of elongation. In this area, outermost tip. It consists of cells that are sloughed off as the cells increase in size through food and water absorption. As root grows through the soil. Its function is to protect the root they grow, they push the root through the soil. meristem. Root hairs are delicate, elongated epidermal cells that occur in a small zone just behind the root’s growing tip. They gener- leaf primordia ally appear as fine down to the naked eye. Their function is to shoot apex increase the root’s surface area and absorptive capacity. Root hairs usually live one or two days. When a plant is transplanted, they are easily torn off or may dry out. Many roots have a naturally occurring symbiotic (mutually beneficial) relationship with mycorrhizae fungi, which improves leaf the plant’s ability to absorb water and nutrients. Types of Roots There are two major types of roots: primary and lateral roots. bud A primary root originates at the lower end of a seedling’s embryo (Figure 1.2). If the primary root continues to elongate downward, becomes the central feature of the root system, and has limited secondary branching, it is called a taproot (Figure 1.4a). Hickory and pecan trees, as well as carrots, have taproots. stem A lateral, or secondary, root is a side or branch root that arises from another root. If the primary root ceases to elongate, and numerous lateral roots develop, a fibrous root system is formed (Figure 1.4b). These lateral roots branch repeatedly to form the network of feeding roots found on most plants. soil line vascular tissue Some plants, such as grasses, naturally produce a fibrous root system. In other cases, severing a plant’s taproot by undercutting it can encourage the plant to produce a fibrous root system. Nurseries use this technique with trees that naturally produce a taproot, because trees with a compact, fibrous root system lateral root are transplanted more successfully. primary root How Roots Grow During early development, a seedling absorbs nutrients and moisture from the soil around the sprouting seed. A band of fertilizer several inches to each side and slightly below newly planted seeds helps early growth of most row crops. As a plant becomes well established, the quantity and distribution of its roots strongly influence its ability to absorb moisture and nutrients. For most plants, the majority of the absorbing (feeder) roots are located in the top 12 inches of soil. Figure 1.1. Principal parts of a vascular plant. (Adapted with per- The soil environment in this region generally is best for root mission from Plant Physiology, The Benjamin/Cummings Publishing Company, Inc., 1991.) growth, with a good balance of fertility, moisture, and air spaces. 1-03 CHAPTER 01 Basic Botany The following factors are important in root growth: often extend well beyond a plant’s drip line (edge of foliage Roots in water-saturated soil do not grow well and ultimately or canopy). Keep this extensive root system in mind when may die due to lack of oxygen. disturbing the soil around existing trees and shrubs. Roots penetrate much deeper in loose, well-drained soil than in heavy, poorly drained soil. Roots as Food A dense, compacted soil layer can restrict or terminate root An enlarged root is the edible portion of several vegetable growth. crops. Sweet potatoes are a swollen tuberous root; and carrots, Container plants not only have a restricted area for root parsnips, salsify, and radishes are elongated taproots. growth, but they are susceptible to cold damage because the limited amount of soil surrounding their roots may not Stems provide adequate insulation. Dark-colored containers may Stems support buds and leaves and serve as conduits for car- also absorb solar radiation in summer, and the heat generated rying water, minerals, and food (photosynthates). The vascular may also damage root systems. system inside the stem forms a continuous pathway from the In addition to growing downward, roots grow laterally and root, through the stem, and finally to the leaves. It is through this system that water and food products move. Structure lateral root Vascular system—This system consists of xylem, phloem, and vascular cambium. It can be thought of as a plant’s plumbing. primary root zone of maturation Xylem tubes conduct water and dissolved minerals; phloem tubes carry food such as sugars. The cambium is a layer of root hairs meristematic tissue that separates the xylem and phloem and produces new xylem and phloem cells. This new tissue is zone of elongation responsible for a stem’s increase in girth. root tip The vascular cambium is important to gardeners. E.g., the meristematic zone root cap cambial tissues on a grafted scion and rootstock need to line up. In addition, careless weed trimming can strip the bark off Figure 1.2. Root structure. (Adapted with permission from Plant Physiology, The Benjamin/Cummings Publishing Company, Inc., 1991.) a tree, thus injuring the cambium and causing the tree to die. The vascular systems of monocots and dicots differ (Figure 1.5). Although both contain xylem and phloem, these structures epidermis are arranged differently in each. In a monocot, the xylem and phloem are paired in bundles, which are dispersed throughout cortex the stem. In a dicot, the vascular system is said to be continu- pericycle ground tissues ous because it forms rings inside the stem. The phloem forms endodermis the outer ring just under the bark in mature woody stems. The xylem forms the inner ring and may be divided into the xylem vascular sapwood and heartwood. Individual rings may be evident in phloem tissue the xylem that correspond to growth events. In temperate zones or climates with pronounced wet and dry seasons, these individual rings can be used to discern the plant’s age and the Figure 1.3. Cross section of a root. (Adapted with permission from Plant environmental conditions that may have caused differing rates Physiology, The Benjamin/Cummings Publishing Company, Inc., 1991.) of yearly growth. Nodes—A node is an area on a stem where buds are located (Figure 1.6). It is a site of great cellular activity and growth where small buds develop into leaves, stems, or flowers. When pruning, it is important to locate a plant’s nodes. Generally, you want to make a pruning cut just above, but not too close to, a node. Pruning in this manner encourages the buds at that node to begin development and ultimately form new stems or leaves. The area between two nodes is called an internode. Its length depends on many factors, including genetics. Several other factors also can influence internode length: (a) taproot (b) fibrous root Figure 1.4. Taproot of a carrot (a) and fibrous root of grass (b). 1-04  Basic Botany CHAPTER 01 Reduced soil fertility decreases internode length, while an phloem phloem application of high-nitrogen fertilizer can greatly increase it. cambium Lack of light increases internode length and causes spindly stems. This situation is known as stretch, or etiolation, and xylem often occurs in seedlings started indoors and in houseplants that do not get enough sunlight. Internode length also varies with the season. Early-season xylem growth has long internodes, while late-season growth gener- ally has much shorter internodes. pith If a stem’s energy is divided among three or four side stems (a) monocot (b) dicot or is diverted into fruit growth and development, internode Figure 1.5. Cross sections of stems: (a) discontinuous vascular system length is shortened. of a monocot stem and (b) continuous vascular system of a woody Plant growth regulator substances and herbicides also can dicot stem. influence internode length. Types of Stems Stems may be long, with great distances between the leaves Stem Terminology and buds (e.g., branches of trees, runners on strawberries) or Shoot—A young stem (one year old or less) with leaves. compressed, with short distances between buds or leaves (e.g., Twig—A young stem (one year old or less) that is in the dormant crowns of strawberry plants, fruit spurs, and African violets). winter stage (has no leaves). Although stems commonly grow aboveground, they sometimes Branch—A stem that is more than one year old, typically with grow belowground in the form of rhizomes, tubers, corms, or lateral stems radiating from it. bulbs. All stems must have buds or leaves to be classified as Trunk—A woody plant’s main stem. stem tissue. Specialized aboveground stems—Some plants have special- ized aboveground stems known as crowns, spurs, or stolons (Figure 1.7). Crowns (on strawberries, dandelions, and African bud violets) are compressed stems with leaves and flowers on short internodes. Spurs are short, stubby side stems that arise from a main stem. They are the fruit-bearing stems on pear, apple, and cherry trees. If severe pruning is done too close to fruit-bearing spurs, they can revert to nonfruiting stems, thus eliminating the year’s node potential fruit crop. Stolons are fleshy or semiwoody, elongated, horizontal internode stems that often lie along the soil surface. Strawberry runners are stolons that have small leaves at the nodes. Roots develop from these nodes, and a daughter plant is formed. This type of vegetative reproduction is an easy way to increase the size of a strawberry patch. Spider plants also produce stolons, which ultimately can become entirely new plants. Figure 1.6. Stem structure. (Adapted with permission from Plant Physiology, The Benjamin/Cummings Publishing Company, Inc., 1991.) Specialized belowground stems—Potato tubers, iris rhizomes, and tulip bulbs are underground stems that store food for the plant (Figure 1.8). It sometimes is difficult to distinguish between roots and stems, but one sure way is to look for nodes. Stems have nodes; roots do not. In potato tubers, for example, the “eyes” are actually the stem’s spur stolon nodes, and each eye contains a cluster of buds. When growing potatoes from “seed” pieces (cut potatoes), it is important that crown each piece contains at least one eye and be about the size of a golf ball so there will be enough energy for early growth of shoots and roots. Figure 1.7. Diversified aboveground stem development. 1-05  CHAPTER 01 Basic Botany leaves leaves Corms are another kind of belowground stem. Although both bulbs and corms are composed of stem tissue, they are not the same. Corms are shaped like bulbs, but do not contain fleshy scales. A corm is a solid, swollen stem with dry, scalelike stem stem leaves. Gladiolus and crocuses produce corms. Other plants (e.g., dahlias and sweet potatoes) produce unicate bulb tunicate bulb underground storage organs called tuberous roots, which often nontunicate nontunicate bulb bulb are confused with bulbs and tubers. However, these are root tissue,tuberous stem and stem tuberous not stem tissue, have neither nodes nor internodes. Stems and Propagationlateral budlateral bud Stems often are usedinternode internode for vegetative plant propagation. Using sections of aboveground stemsnodethat contain node nodes and inter- nodes is an effective way to propagate many ornamental plants. These stem cuttings produce rootsold old corm andcorm eventually new plants. Belowground stems also are good propagative tissues. You can divide rhizomes into pieces, remove small bulblets or rhizome rhizome tuberoustubers stem tubers cormels fromcorm the parent,corm and cut tubers into pieces containing lateral bud eyes and nodes. All of these tissues will produce new plants. internode Types of Plants and Their Stems node Trees generally have one, but occasionally several, main trunks, which usually are more than 12 feet tall when mature. old corm In contrast, shrubs generally have several main stems, which usually are less than 12 feet tall when mature. Most fruit trees, ornamental trees, and shrubs have woody tuberous stem tubers corm stems. These stems contain relatively large amounts of hardened Figure 1.8. Diversified belowground stem development. xylem tissue in the central core (heartwood or sapwood). lateral bud Herbaceous or succulent stems contain only a little xylem internode tissue and usually live for only one growing season. In peren- Rhizomes resemble stolons because they grow horizon- tally from plant to plant. Some node rhizomes are compressed and nial plants, new herbaceous stems develop from the crown fleshy (e.g., iris), while others are slender and have elongated (root–stem interface) each year. internodes (e.g., bentgrass). oldJohnsongrass corm is an insidious weed Canes are stems with relatively large pith. They usually live principally because of the spreading capability of its rhizomes. only one or two years. Tulips, lilies, daffodils, and onions produce bulbs, which are Examples of plants with canes include roses, grapes, black- corm shortened, compressed underground stems surrounded by berries, and raspberries. For fruit production, it is important fleshy scales (leaves) that envelop a central bud at the tip of the to know which canes to prune, how to prune them, and when stem. In November, you can cut a tulip or daffodil bulb in half to prune them. and see all of the flower parts in miniature. A vine is a plant with long, trailing stems. Some vines grow After a bulb-producing plant flowers, its phloem transports along the ground, while others must be supported by another food reserves from its leaves to the bulb’s scales. When the plant or structure. Twining vines circle a structure for support. bulb begins growing in the spring, it uses the stored food. For Some circle clockwise (e.g., hops and honeysuckle), while others this reason, it is important not to remove the leaves from daf- circle counterclockwise (e.g., pole beans and Dutchman’s pipe fodils, tulips, and other bulb-producing plants until after they vine). Climbing vines are supported either by aerial roots (e.g., have turned yellow and withered. At that time, these plants English ivy and poison ivy), by slender tendrils that encircle a have finished producing the food that will be used for next supporting object (e.g., cucumbers, gourds, grapes, and pas- year’s flowering. sionflowers), or by tendrils with adhesive tips (e.g., Virginia There are two types of bulbs: tunicate and nontunicate and Japanese creeper). In temperate areas both woody and (Figure 1.8). Tunicate bulbs (e.g., daffodils, tulips, and onions) herbaceous trailing plants are called vines, but in the tropics, have concentric scales, actually modified leaves. It helps protect woody trailing plants are called “lianas.” the bulb from damage during digging and from drying out once it is out of the soil. Nontunicate, or scaly, bulbs (e.g., lilies) have individual scalelike modified leaves. They are very susceptible to damage and drying out, so handle them very carefully. 1-06  Basic Botany CHAPTER 01 Stems as Food requirement, varies for different plants. Forsythia, for example, The edible portion of several cultivated plants, such as requires a relatively short rest period and grows at the first sign asparagus and kohlrabi, is an enlarged, succulent stem. The of warm weather. Many peach varieties, on the other hand, edible parts of broccoli are composed of stem tissue, flower require 700 to 1,000 hours of temperatures below 45°F. During buds, and a few small leaves. The edible tuber of a potato is a rest, dormant buds can withstand very low temperatures, but fleshy underground stem. And, although the name suggests after the rest period is satisfied, they are more susceptible to otherwise, the edible part of cauliflower actually is proliferated damage by cold temperatures or frost. stem tissue. A leaf bud is composed of a short stem with embryonic leaves. Leaf buds often are less plump and more pointed than flower buds (Figure 1.9). Buds A flower bud is composed of a short stem with embryonic A bud is an undeveloped shoot from which leaves or flower flower parts. In the case of fruit crops, flower buds sometimes parts grow. The buds of temperate-zone trees and shrubs typi- are called fruit buds. This terminology is inaccurate, however; cally develop a protective outer layer of small, leathery scales. although flowers have the potential to develop into fruits, they Annual plants and herbaceous perennials have naked buds with may not do so because of adverse weather conditions, lack of green, somewhat succulent, outer leaves. pollination, or other unfavorable circumstances. Buds of many plants require exposure to a certain number of days below a critical temperature before resuming growth Location in the spring. This period, often referred to as rest or chilling Buds are named for their location on the stem (Figure 1.10). Terminal buds are located at the apex (tip) of a stem. Lateral (axillary) buds are located on the sides of a stem and usually leaf bud arise where a leaf meets a stem (an axil). In some instances, an axil contains more than one bud. flower bud Adventitious buds arise at sites other than the terminal or axillary position. They may develop from roots, a stem inter- node, the edge of a leaf blade, or callus tissue at the cut end of a stem or root. Adventitious buds allow stem, leaf, and root cuttings to develop into entirely new plants. Buds as Food Enlarged buds or parts of buds form the edible portion of some horticultural crops. Cabbage and head lettuce are examples of unusually large terminal buds. Succulent axillary buds are the edible part of Brussels sprouts. In the case of globe artichoke, the fleshy basal portion of the flower bud’s bracts is Figure 1.9. Elm leaf and flower buds. eaten, along with its solid stem. Broccoli is the most important horticultural plant with edible flower buds. In this case, portions of the stem, as well as small leaves associated with the flower terminal buds, are eaten. bud Leaves Function and Structure The principal function of leaves is to absorb sunlight to man- lateral ufacture plant sugars through a process called photosynthesis. twig (axillary) Leaf surfaces are flattened to present a large area for efficient light absorption. The blade, or lamina, is the expanded thin bud structure on either side of the midrib and usually is the largest, most conspicuous part of a leaf (Figure 1.11). A leaf is held away from its stem by a stemlike appendage called a petiole, and the base of the petiole is attached to the stem at a node. Petioles vary in length or may be lacking entirely, in which case the leaf blade is described as sessile, or stalkless. Figure 1.10. Bud location. 1-07 CHAPTER 01 Basic Botany The node where a petiole meets a stem is called a leaf axil. The cuticle is part of the epidermis. It produces a waxy layer The axil contains single buds or bud clusters, referred to as called cutin, which protects the leaf from dehydration and dis- axillary buds. They may be either active or dormant; under the ease. The amount of cutin on a leaf increases with increasing right conditions, they will develop into stems or leaves. light intensity. For this reason, when moving plants from shade A leaf blade is composed of several layers (Figure 1.12). On into full sunlight, do so gradually over a period of a few weeks. the top and bottom is a layer of thick, tough cells called the epi- This gradual exposure to sunlight allows the cutin layer to build dermis. Its primary function is to protect the other layers of leaf up and protect the leaves from rapid water loss or sunscald. tissue. The arrangement of epidermal cells determines the leaf ’s The waxy cutin also repels water. For this reason, many surface texture. Some leaves, such as those of African violets, pesticides contain a spray additive to help the product adhere have hairs (pubescence), which are extensions of epidermal cells to, or penetrate, the cutin layer. that make the leaves feel like velvet. Special epidermal cells called guard cells open and close in response to environmental stimuli such as changes in weather and light. They regulate the passage of water, oxygen, and carbon leaf axil with dioxide into and out of the leaf through tiny openings called axillary bud stomata. In most species, the majority of the stomata are located on the underside of leaves. Conditions that would cause plants to lose a lot of water (high temperature, low humidity) stimulate guard cells to close. In mild weather, they remain open. Guard cells also close in the blade absence of light. Located between the upper and lower epidermis is the midrib mesophyll. It is divided into a dense upper layer (palisade meso- phyll) and a lower layer that contains lots of air space (spongy mesophyll). Located within the mesophyll cells are chloroplasts, petiole where photosynthesis takes place. node Types of Leaves There are many kinds of plant leaves. The most common stem and conspicuous leaves are referred to as foliage and are the primary location of photosynthesis. However, there are many Figure 1.11. Leaf parts. (Adapted with permission from Plant other types of modified leaves: Physiology, The Benjamin/Cummings Publishing Company, Inc., 1991.) Scale leaves (cataphylls) are found on rhizomes and buds, which they enclose and protect. cuticle Seed leaves (cotyledons) are found on embryonic plants. upper They store food for the developing seedling. epidermis Spines and tendrils, such as those on barberry and pea plants, palisade protect a plant or help support its stems. layer Storage leaves, such as those on bulbous plants and succu- lents, store food. Bracts often are brightly colored. For example, the showy structures on dogwoods and poinsettias are bracts, vascular not petals. bundle Venation spongy