Topic 6 - Botany (Morphology of stems) PDF

PBS 101.23 TOPIC 6: MORPHOLOGY OF STEMS Outline of Topics: a. General Structure of Stems b. External Structure of Stems c. Internal Structure of Stems d. Stem Modifications e. Uses of Stems General Structure of Stems...

PBS 101.23 TOPIC 6: MORPHOLOGY OF STEMS Outline of Topics: a. General Structure of Stems b. External Structure of Stems c. Internal Structure of Stems d. Stem Modifications e. Uses of Stems General Structure of Stems The plumule develops to form the stem. Thus stem is an aerial part of the plant. It consists of axis and the leaves. Stem has got the following characteristics: 1. It is ascending axis of the plant and phototropic in nature. 2. It consists of nodes, internodes and buds. 3. It gives rise to branches, leaves and flowers. 4. Stems may be aerial, sub-aerial and underground. Depending upon the presence of mechanical tissues, the stems may be weak, herbaceous or woody. [A] Weak stems: When the stems are thin and long, they are unable to stand erect, and hence may be one of the following types: (a) Creepers or Prostate stem: When they grow flat on the ground with or without roots, e.g. grasses,cgokharu, etc. (b) Climbers: These are too weak to stand alone. They climb on the support with the help of tendrils, hooks, prickles or roots, e.g. Piper betel, Piper longum. (c) Twinners: These coil the support and grow further. They are thin and wiry, i.e. ipomoea. [B] Herbaceous and woody stems: These are the normal stems and may be soft or hard and woody, i.e. sunflower, sugarcane, mango, etc. 1. Produce leaves and exposes them properly to sunlight for carrying out photosynthesis. 2. Conducts water and minerals from roots to leaves and buds. 3. Foods produced by leaves are transported to nongreen parts of the plant. 4. Produce flowers and fruits for pollination and seal dispersal. 5. Depending upon the environment it gets suitably modified to perform special functions like storage of foods, means of propagation, etc. External Structure of Stems A woody twig consists of an axis with attached leaves (Fig. 6.1). If the leaves are attached to the twig alternately or in a spiral around the stem, they are said to be alternate, or alternately arranged. If the leaves are attached in pairs, they are said to be opposite, or oppositely arranged, or if they are in whorls (groups of three or more), their arrangement is whorled. The area, or region (not structure), of a stem where a leaf or leaves are attached is called a node, and a stem region between nodes is called an internode. A leaf usually has a flattened blade and in most cases is attached to the twig by a stalk called the petiole. Each angle between a petiole and the stem contains a bud. The angle is called an axil, and the bud located in the axil is an axillary bud. In flowering plants (angiosperms), axillary buds may become branches, or they may contain tissues that will develop into the next season’s flowers. Most buds are protected by one to several bud scales, which fall off when the bud tissue starts to grow. There often (but not always) is a terminal bud present at the tip of each twig. A terminal bud usually resembles an axillary bud, although it is often a little larger. Unlike axillary buds, terminal buds do not become separate branches, but, instead, the meristems within them normally produce tissues that make the twig grow longer during the growing season. The bud scales of a terminal bud leave tiny scars around the twig when they fall off in the spring. Counting the number of groups of bud scale scars on a twig can tell one how old the twig is. Sometimes other scars of different origin also occur on a twig. These scars come from a leaf that has stipules at the base of the petiole. Stipules are paired, often somewhat leaflike, appendages that may remain throughout the life of the leaf. In some plants, they fall off as the buds expand in the spring, leaving tiny stipule scars. The stipule scars may resemble a fine line encircling the twig, or they may be very inconspicuous small scars on either side of the petiole base. Deciduous trees and shrubs (those that lose all their leaves annually) characteristically have dormant axillary buds with leaf scars left below them after the leaves fall. Tiny bundle scars, which mark the location of the water-conducting and food-conducting tissues, are usually visible within the leaf scars. Internal Structures of Stem There is an apical meristem (tissue in which cells actively divide) at the tip of each stem, and it is this meristem that contributes to an increase in the length of the stem. The apical meristem is dormant before the growing season begins. It is protected by bud scales of the bud in which it is located and to a certain extent by leaf primordia (singular: primordium), the tiny embryonic leaves that will develop into mature leaves after the bud scales drop off and growth begins. The apical meristem in the embryonic stem of a seed is also dormant until the seed begins to germinate. When a bud begins to expand or a seed germinates, the cells of the apical meristem undergo mitosis, and soon three primary meristems develop from it (see Fig. 6.2). The outermost of these primary meristems, the protoderm, gives rise to the epidermis. Although there are exceptions, the epidermis is typically one cell thick and usually becomes coated with a thin, waxy, protective layer, the cuticle. A cylinder of strands constituting the procambium appears to the interior of the protoderm. (The procambium produces waterconducting primary xylem cells and primary phloem cells that have several functions, including the conduction of food.)  The remainder of the meristematic tissue, called ground meristem, produces two tissues composed of parenchyma cells. The parenchyma tissue in the center of the stem is the pith. Pith cells tend to be very large and may break down shortly after they are formed, leaving a cylindrical, hollow area. Even if they do not break down early, they may eventually be crushed as new tissues produced by other meristems add to the girth of the stem, particularly in woody plants. The other tissue produced by the ground meristem is the cortex. The cortex may become more extensive than the pith, but in woody plants, it, too, eventually will be crushed and replaced by new tissues produced from within. The parenchyma of both the pith and the cortex function in storing food or sometimes, if chloroplasts are present, in manufacturing it. All five of the tissues produced by this apical meristem complex (epidermis, primary xylem, primary phloem, pith, and cortex) arise while the stem is increasing in length and are called primary tissues. As these primary tissues are produced, the leaf primordia and the bud primordia (embryonic buds in the axils of the leaf primordia) develop into mature leaves and buds (Fig. 6.2).  A narrow band of cells between the primary xylem and the primary phloem may retain its meristematic nature and become the vascular cambium, one of the two lateral meristems. The vascular cambium is often referred to simply as the cambium. The cells of the cambium continue to divide indefinitely, with the divisions taking place mostly in a plane parallel to the surface of the plant. The secondary tissues produced by the vascular cambium add to the girth of the stem instead of to its length (Fig. 6.4). Cells produced by the vascular cambium become tracheids, vessel elements, fibers, or other components of secondary xylem (inside of the meristem, toward the center), or they become sieve tube members, companion cells, or other components of secondary phloem (outside of the meristem, toward the surface). The functions of these secondary tissues are the same as those of their primary counterparts—secondary xylem conducts water and soluble nutrients, while secondary phloem conducts, in soluble form, food manufactured by photo synthesis throughout the plant.  In many plants, especially woody species, a second cambium arises within the cortex or, in some instances, develops from the epidermis or phloem. This is called the cork cambium, or phellogen. The cork cambium produces boxlike cork cells, which become impregnated with suberin, a waxy substance that makes the cells impervious to moisture. The cork cells, which are produced annually in cylindrical layers, die shortly after they are formed. The cork cambium may also produce parenchyma-like phelloderm cells to the inside. Cork tissue makes up the outer bark of woody plants; it functions in reducing water loss and in protecting the stem against mechanical injury. Cork tissue cuts off water and food supplies to the epidermis, which soon dies and is sloughed off. In fact, if the cork were to be formed as a solid cylinder covering the entire stem, vital gas exchange with the interior of the stem would not be possible. In young stems, such gas exchange takes place through the stomata, located in the epidermis. As woody stems age, lenticels develop beneath the stomata. As cork is produced, the parenchyma cells of the lenticels remain, so that exchange of gases (e.g., oxygen, carbon dioxide) can continue through spaces between the cells. Lenticels occur in the fissures of the bark of older trees and often appear as small bumps on younger bark. In birch and cherry trees, the lenticels form conspicuous horizontal lines. Steles – Primary xylem, primary phloem, and the pith, if present, make up a central cylinder called the stele in most of the younger and a few older stems and roots. The simplest form of stele, called a protostele, consists of a solid core of conducting tissues in which the phloem usually surrounds the xylem. Protosteles were common in primitive seed plants that are now extinct and are also found in whisk ferns, club mosses, and other relatives of ferns. Siphonosteles, which are tubular with pith in the center, are common in ferns. Most present-day flowering plants and conifers have eusteles in which the primary xylem and primary phloem are in discrete vascular bundles, as discussed in the section “Herbaceous Dicotyledonous Stems.” Herbaceous Dicotyledonous Stems In general, plants that die after going from seed to maturity within one growing season (annuals) have green, herbaceous (nonwoody) stems. Most monocots are annuals, but many dicots (discussed next) are also annuals. The tissues of annual dicots are largely primary, although cambia (plural of cambium) may develop some secondary tissues. Herbaceous dicot stems (Fig. 6.5) have discrete vascular bundles composed of patches of xylem and phloem. The vascular bundles are arranged in a cylinder that separates the cortex from the pith, although in a few plants (e.g., foxgloves), the xylem and the phloem are produced as continuous rings (cylinders) instead of in separate bundles.  The procambium produces only primary xylem and phloem, but later, a vascular cambium arises between these two primary tissues and adds secondary xylem and phloem to the vascular bundles. In some plants, the cambium extends between the vascular bundles, appearing as a narrow ring, producing not only the conducting tissues within the bundles but also the parenchyma cells between them. In other plants, the cambium is not in an uninterrupted cylinder but is instead confined to the bundles, each of which has its own small band of cambium between the xylem and phloem. Woody Dicotyledonous Stems In the early stages of development, the primary tissues of stems of young herbaceous dicots, woody dicots, and cone-bearing trees are all arranged in a similar fashion. In woody plants, however, obvious differences begin to appear as soon as the vascular cambium and the cork cambium develop. The most conspicuous differences involve the secondary xylem, or wood, as it is best known (Fig. 6.6). Some tropical trees (e.g., ebony), in which both the vascular cambium and the cork cambium are active all year, produce an ungrained, uniform wood. The wood of most trees, however, is produced seasonally. In trees of temperate climates, virtually all growth takes place during the spring and summer and then ceases until the following spring.  When the vascular cambium of a typical broadleaf tree first becomes active in the spring, it usually produces relatively large vessel elements of secondary xylem; such xylem is referred to as spring wood. As the season progresses, the vascular cambium may produce vessel elements whose diameters become progressively smaller in each succeeding series of cells produced, or there may be fewer vessel elements in proportion to tracheids produced until tracheids (and sometimes fibers) predominate. The xylem that is produced after the spring wood, and which has smaller or fewer vessel elements and larger numbers of tracheids, is referred to as summer wood. Over a period of years, the result of this type of switch between the early spring and the summer growth is a series of alternating concentric rings of light and dark cells. One year’s growth of xylem is called an annual ring. In conifers, the wood consists mostly of tracheids, with vessels and fibers being absent. Annual rings are still visible, however, because the first tracheids produced in the spring are considerably larger and lighter in color than those produced later in the growing season. Note that an annual ring normally may contain many layers of xylem cells and it is all the layers produced in one growing season that constitute an annual ring—not just the dark layers. The bulk of a tree trunk consists of annual rings of wood. The annual rings not only indicate the age of the tree (because, normally, only one is produced each year), but they can also tell something of the climate and other conditions that occurred during the tree’s lifetime (Fig. 6.7). For example, if the rainfall during a particular year is higher than normal, the annual ring for that year will be wider than usual because of increased growth. Sometimes, caterpillars or locusts will strip the leaves of a tree shortly after they have appeared. This usually results in a narrow annual ring, because very little growth can take place under such conditions.  If there is a fire that doesn’t result in the death of the tree, it may be possible to determine when the fire occurred, because the burn scar may appear next to a given ring. The most recent season’s growth is next to the vascular cambium, and one need only count the rings back from the cambium to determine the actual year of the fire. It is not necessary to cut down a tree to determine its age. Instead, botanists and foresters can employ an increment borer to find out how old a woody plant is. This device, which resembles a piece of pipe with a handle on one end, removes a plug of wood from the tree perpendicular to the axis, and the annual rings in the plug can then be counted. The small hole left in the tree can be treated with a disinfectant to prevent disease and covered up without harm to the tree. A count of annual rings has produced some red faces on at least one occasion. The Hooker Oak, which was named in honor of Sir Joseph Hooker, a famous British botanist who once examined it, was located in the community of Chico, California. Until its demise in 1977, thousands of visitors from all over the world visited the huge oak, which provided enough shade for 9,000 people on a summer day. A plaque indicating the tree to be over 1,000 years old was located beneath the tree. A count of rings after its death, however, revealed that the Hooker Oak was less than 300 years old. When a tree trunk is examined in transverse, or cross section, fairly obvious lighter streaks or lines can be seen radiating out from the center across the annual rings. These lines, called vascular rays, consist of parenchyma cells that may remain alive for 10 or more years. Their primary function is the lateral conduction of nutrients and water from the stele, through the xylem and phloem, to the cortex, with some cells also storing food. Any part of a ray within the xylem is called a xylem ray, while its extension through the phloem is called a phloem ray. In trees such as basswood (Tilia), some of the phloem rays, when observed in cross section, flare out from a width of two or three cells near the cambium to many cells wide in the part next to the cortex (see Fig. 6.6). In radial section, rays may be from two or three cells to 50 or more cells deep, but the majority of rays in both xylem and phloem are one or two cells wide. Ray cells can be seen in cross section if a woody stem is cut or split lengthwise along a ray (Fig. 6.8). Another view of rays (in tangential section) is obtained when the stem is cut at a tangent (i.e., cut lengthwise and off center) (see Fig. 6.17). As a tree ages, the protoplasts of some of the parenchyma cells that surround the vessels and tracheids grow through the pits in the walls of these conducting cells and balloon out into the cavities. As the protoplasm continues to expand, much of the cavity of the vessel or tracheid becomes filled. Such protrusions, called tyloses (singular: tylosis), prevent further conduction of water and dissolved substances. When this occurs, resins, gums, and tannins begin to accumulate, along with pigments that darken the color of the wood. This older, darker wood at the center is called heartwood, while the lighter, still-functioning xylem closest to the cambium is called sapwood (Fig. 6.9). Except for giving strength and support, the heartwood is not of much use to the tree, because it can no longer conduct materials. A tree may live and function perfectly well after the heartwood has rotted away and left the interior hollow. It is even possible to remove part of the sapwood and other tissues and apparently not affect the tree very much, as has been done with giant trees, such as the coastal redwoods of California, where holes big enough to drive a car through have been cut out without killing the trees (Fig. 6.10).  Sapwood forms at roughly the same rate as heartwood develops, so there is always enough “plumbing” for the vital conducting functions. The relative widths of the two types of wood, however, vary considerably from species to species. For example, in the golden chain tree (a native of Europe and a member of the Legume Family), the sapwood is usually only one or two rings wide, while in several North American trees (e.g., maple, ash, and beech), the sapwood may be many rings wide. Pines and other cone-bearing trees have xylem that consists primarily of tracheids; no fibers or vessel elements are produced. Because it has no fibers, the wood tends to be softer than wood with fibers and is commonly referred to as softwood, while the wood of woody dicot trees is called hardwood. In many cone-bearing trees, resin canals are scattered not only through the xylem but throughout other tissues as well. These canals are tubelike and may or may not be branched; they are lined with specialized cells that secrete resin into their cavities (Fig. 6.11). Although resin canals are commonly associated with conebearing trees, they are not confined to them. Tropical flowering plants, such as olibanum and myrrh trees, have resin ducts in the bark that produce the soft resins frankincense and myrrh of biblical note. Just beneath the epidermis is a hypodermis, consisting of one to several layers of thick-walled cells. The veins and their associated tissues are surrounded by an endodermis, and the mesophyll cells do not have the obvious air spaces typical of the spongy mesophyll of the leaves of flowering plants. Conspicuous resin canals develop in the mesophyll. These resin canals, which are found throughout other parts of the plant as well, consist of tubes lined with special cells that secrete resin. Resin is aromatic and antiseptic and prevents the development of fungi; it also deters insect attacks. Other conifers apparently produce resin canals in response to injury. Pine fascicles usually abcise within 2 to 5 years of their maturing, but those of bristlecone pines persist for up to 30 years. The fascicles are lost a few at a time, so that some functional leaves are always present on a healthy tree. While the vascular cambium is producing secondary xylem to the inside, it is also producing secondary phloem to the outside. The term bark is usually applied to all the tissues outside the cambium, including the phloem. Some scientists distinguish between the inner bark, consisting of primary and secondary phloem, and the outer bark (periderm), consisting of cork tissue and cork cambium. Despite the presence of fibers, the thin-walled conducting cells of the phloem usually are not able to withstand for many seasons the pressure of thousands of new cells added to their interior, and the older layers become crushed and functionless. The parenchyma cells of the cortex to the outside of the phloem also function only briefly because they, too, become crushed or sloughed off. Before they disappear, however, the cork cambium begins its production of cork, and because new xylem and phloem tissues produced by the vascular cambium arise to the inside of the older phloem, the mature bark may consist of alternating layers of crushed phloem and cork. The younger layers of phloem nearest to the cambium transport, via their sieve tubes, sugars and other substances in solution from the leaves where they are made to various parts of the plant, where they are either stored or used in the process of respiration. The presence of sugar in the phloem was recognized in the past by Native Americans. Some stripped the young phloem and cambium from Douglas fir trees and used the dried strips as food for winter and in emergencies. Specialized cells or ducts called laticifers are found in about 20 families of herbaceous and woody flowering plants. These cells are most common in the phloem but occur throughout all parts of the plants. The laticifers, which resemble vessels, form extensive branched networks of latex-secreting cells originating from rows of meristematic cells. Unlike vessels, however, the cells remain living and may have many nuclei. Latex is a thick fluid that is white, yellow, orange, or red in color and consists of gums, proteins, sugars, oils, salts, alkaloidal drugs, enzymes, and other substances. Its function in the plant is not clear, although some believe it aids in closing wounds. Some forms of latex have considerable commercial value. Of these, rubber is the most important. Amazon Indians utilized rubber for making balls and containers hundreds of years before Pará rubber trees were cultivated for their latex. The chicle tree produces a latex used in the making of chewing gum. Several poppies, notably the opium poppy, produce latex containing, important drugs, such as morphine and its derivative, known as heroin. Other well-known latex producers include milkweeds, dogbanes, and dandelions. Monocotyledonous Stems Most monocots (e.g., grasses, lilies) are herbaceous plants that do not grow tall. The stems have neither a vascular cambium nor a cork cambium and thus produce no secondary vascular tissues or cork. As in herbaceous dicots, the surfaces of the stems are covered by an epidermis, but the xylem and phloem tissues produced by the procambium appear in cross section as discrete vascular bundles scattered throughout the stem instead of being arranged in a ring (Fig. 6.12).  Each bundle, regardless of its specific location, is oriented so that its xylem is closer to the center of the stem and its phloem is closer to the surface. In a typical monocot, such as corn, a bundle’s xylem usually contains two large vessels with several small vessels between them (Fig. 6.13). The first-formed xylem cells usually stretch and collapse under the stresses of early growth and leave an irregularly shaped air space toward the base of the bundle; the remnants of a vessel are often present in this air space. The phloem consists entirely of sieve tubes and companion cells, and the entire bundle is surrounded by a sheath of thicker-walled sclerenchyma cells. The parenchyma tissue between the vascular bundles is not separated into cortex and pith in monocots, although its function and appearance are the same as those of the parenchyma cells in cortex and pith. In a corn stem, there are more bundles just beneath the surface than there are toward the center. Also, a band of sclerenchyma cells, usually two or three cells thick, develops immediately beneath the epidermis, and parenchyma cells in the area develop thicker walls as the stem matures. The concentration of bundles, combined with the band of sclerenchyma cells beneath the epidermis and the thickerwalled parenchyma cells, all contribute to giving the stem the capacity to withstand stresses resulting from summer storms and the weight of the leaves and the ears of corn as they mature. In wheat, rice, barley, oats, rye, and other grasses, there is an intercalary meristem (discussed in Chapter 4) at the base of each internode; like the apical meristem, it contributes to increasing stem length. Although the stems of such plants elongate rapidly during the growing season, growth is columnar (i.e., there is little difference in diameter between the top and the bottom) because there is no vascular cambium producing tissues that would add to the girth of the stems. Palm trees, which differ from most monocots in that they often grow quite large, do so primarily as their parenchyma cells continue to divide and enlarge without a true cambium developing. Several popular house plants (e.g., ti plants, Dracaena, Sansevieria) are monocots in which a secondary meristem develops as a cylinder that extends throughout the stem. Unlike the vascular cambium of dicots and conifers, this secondary meristem produces only parenchyma cells to the outside and secondary vascular bundles to the inside.  Several commercially important cordage fibers (e.g., broomcorn, Mauritius and Manila hemps, sisal) come from the stems and leaves of monocots, but the individual cells are not separated from one another by retting (a process that utilizes the rotting power of microorganisms thriving under moist conditions to break down the thin-walled parenchyma cells) as they are when fibers from dicots are obtained. Instead, during commercial preparation, entire vascular bundles are scraped free of the surrounding parenchyma cells by hand; the individual bundles then serve as unit “fibers.” If such fibers are treated with chemicals or bleached, the cementing middle lamella between the cells breaks down. Monocot fibers are not as strong or as durable as most dicot fibers. Stem Modifications I. Underground modifications of stems Underground modifications of stems are of the following types: 1. Rhizome 2. Tuber 3. Bulb 4. Corm. 1. Rhizomes: Grow horizontal under the soil. They are thick and are characterized by the presence of nodes, internodes and scale leaves. They also possess bud in the axil of the scale leaves, e.g. ginger, turmeric, rhubarb, male fern, etc. 2. Tubers: Tubers are characterized by the presence of ‘eyes’ from the vegetative buds which grow further and develop into a new plant. Tubers are the swollen underground structure of the plant, e.g. potato, jalap, aconite, etc. 3. Bulb: In this case, the food material is stored in fleshy scales that overlap the stem. They are present in the axils of the scales, and few of them develop into new plant in the spring season at the expense of stored food material in the bulb. Adventitious roots are present at the base of the bulb. The reserve food material formed by the leaves is stored at their bases, and the new bulbs are produced next year, e.g. garlic, squill and onion. 4. Corm: Corms are generally stout, and grow in vertical direction. They bear bud in the axil of the scaly leaves, and these buds then develop further to form the new plant. Adventitious roots are present at the base of the corm, e.g. saffron, colchicum, dioscorea, etc. II. Sub-aerial modifications of stems: These include (1) Runner, (2) Stolon, (3) Offset and (4) Sucker. 1. Runner: These creep on the ground and root at the nodes. Axillary buds are also present, e.g. strawberry, pennywort. 2. Stolon: These are lateral branches arising from the base of the stems which grow horizontally. They are characterized by the presence of nodes and internodes. Few branches growing above the ground develop into a new plant, e.g. glycyrrhiza, arrowroot, jasmine, etc. 3. Offsets: These originate from the axil of the leaf as short, thick horizontal branches and also characterized by the presence of rosette type leaves and a cluster of roots at their bottom, e.g. aloe, valerian. 4. Sucker: These are lateral branches developed from underground stems. Suckers grow obliquely upwards, give rise to a shoot which develop further into a new plant, e.g. mentha species, chrysanthemum, pineapple, banana, etc. III. Aerial modification of stems As the name indicates they grow into the air above the soil to a certain height, as follows: 1. Phylloclades: At times, the stem becomes green and performs the function of leaves. Normally this is found in the plants growing in the desert (xerophytes). Phylloclades are characterized by the presence of small leaves or pointed spines, e.g. opuntia, ruscus, euphorbia, etc. Cladode is a type of phylloclade with one internode, i.e. asparagus. 2. Thorns and prickles: This is another type of aerial modification meant for protection. Thorns are hard, pointed, straight structures, such as duranta, lemon, etc. Prickles and thorns are identical in function. Prickles get originated from outer tissues of the stem. Thus, they are superficial outgrowths. Prickles are sharp, pointed and curved structures. They are scattered all over the stem. Rose, smilax can be quoted as examples of the same. 3. Stem tendrils: In certain plants, the buds develop into tendrils for the purpose of support. Terminal buds in case of vitis, axillary bud in case of passiflora are suitable examples. 4. Bulbils: These are modifications of floral buds meant for vegetative propagation, such as Dioscorea and Agave. Uses of stems Depending upon the structural and chemical contents, stems are used for various purposes. 1. Underground stems in their various forms are either used as food spices or for culinary purposes like, potato, amorphophalus, colocasia, garlic, ginger and onion. 2. Jowar, rice and other stems are used as fodder. 3. Stems of jute, hemp and flax as sources of industrial fibres used for various purposes. 4. Sugarcane stems are used as source of sucrose while latex from stems of Hevea brasiliensis is used as rubber. 5. Woods from stems of several plants are used as drugs like quassia, guaicum, sandalwood, etc. 6. The stems of several plants are injured to produce gums for their multiple industrial uses like gum- acacia, gum-tragacanth, gum-sturculia, etc. REFERENCES: Names: Bidlack, James E., author. | Jansky, Shelley. Title: Introductory plant biology / James E. Bidlack, University of Central Oklahoma, Shelley H. Jansky, University of Wisconsin - Madison. Other titles: Stern’s introductory plant biology Description: 14th edition. | New York, NY : McGraw-Hill, 2017. | “Stern’s introductory plant biology, 14th edition”—T.p. verso. Identifiers: LCCN 2016044453 | ISBN 9781259682742 (alk. paper) Subjects: LCSH: Botany. Classification: LCC QK47.S836 2017 | DDC 580—dc23 LC record available at https://lccn.loc.gov/2016044453 Textbook of Pharmacognosy and Phytochemistry Shah and Seth ELSEVIER A division of Reed Elsevier India Private Limited Published by Elsevier, a division of Reed Elsevier India Private Limited Registered Office: Gate No. 3, Building No. A-1, 2, Industrial Area, Kalkaji, New Delhi-110019 Corporate Office: 14th Floor, Building