Fundamentals of Plant Morphology and Anatomy (Botany 0101) PDF

Fundamentals of plant morphology and anatomy (Botany 0101) Prepared by Dr. Ahmed Gad  Internal factors that control Germination: - 1- Seed Dormancy  Direct germination of seeds immediately after their formation while they are still on the mother...

Fundamentals of plant morphology and anatomy (Botany 0101) Prepared by Dr. Ahmed Gad  Internal factors that control Germination: - 1- Seed Dormancy  Direct germination of seeds immediately after their formation while they are still on the mother plant ( Phizophora) is called viviparous plants.  Germination after maturity if suitable conditions are available. Economic plants.  Some seeds do not germinate until a period of time after ripening ( this period ranges from weeks to more than a hundred years ).  Failure to germinate due to internal conditions is called dormancy ( rest period ), and dormancy is attributed to one or more of the following reasons: 1. The hardness of testsa, the seed coat, or fruit coat to a degree that prevents water from penetrating into the embryo, such as seeds of Canna indica , Amarantrus sp. , and sweet potato seeds ( treatment: remove the coat or puncture it, treat the seed with sulfuric acid, and in cold regions bury it in the soil during the winter, so that it dries out and its coat tears ). 2. The husk is impermeable to gases, which prevents oxygen from entering the husk, and also prevents the leakage of CO2 resulting from respiration, like many seeds of plants of the Asteraceae family ( these seeds germinate over time as a result of the seeds decomposing thanks to microorganisms or by the seeds being exposed to weather changes or chemical substances ). 3. Incomplete embryo formation requires some Ranunculus plants. 4. The embryo is complete, but it needs a period after ripening for some chemical and physical changes to occur ( and this type can be treated with chemical treatments ) , for example, the rose Rosa sp. , and the apple Pyrus malus 5. The presence of inhibitory substances in the grain that prevent germination, such as sunflower, or these substances are found in the endosperm, such as the iris plant Iris sp. , or in short plants such as cabbage, lettuce (the seeds fall and change the water where the inhibitory substances are soluble).  2- Seed viability The period during which seeds retain their viability varies depending on the type of plant ( it should be noted that the period during which seeds retain their viability (longevity) differs from the dormancy period) , but the longer the dormancy period, the longer the seed’s ability to retain its viability.  Examples: 1. Oxails sp. seeds germinate after dispersal and are damaged if exposed to dry air. 2. Willow Solix sp. can retain its vitality for several days. 3. Populus sp. and trees retain their vitality for several years, for example cassia retains its vitality for about 160 years ( the trunk is impermeable to water ).  Factors affecting seed vitality: 1. plant vigour 2. Environmental conditions that affected the seeds during formation. 3. Seeds germinated before maturity gives a weak plant. 4. Seed storage conditions ( temperature , humidity , ventilation ). 5. Seed age.  4- Germination of date palm ( phaenix dactylifera ) seeds The testa: a thin, hard corky layer that adheres to the hard horny endosperm. Horny Endosperm contains hemicellulose. Germination takes a month. The radicle first appears, driven by the cotyledon, which is located along its length and inside it is the plumule in a part known as the cotyledon sheath. The other end of the cotyledon remains inside the seed, attached to the endosperm, and secretes enzymes to dissolve and analyze the stored food. The part that absorbs the food and delivers it to the embryo is known as the absorbing part. The cotyledon in dates works to digest and absorb the food of the endosperm and deliver it to the radicle and the feather. It also carries the radicle and the feather out of the seed. It also places the radicle and the feather at the appropriate depth for germination. Ground germination. Seed = cotyledon + horny endosperm + embryo (one cotyledon envelops the radical and the plumule and the sheath of each of the radical and the plumule) Testa Embryo position First stage: emergence of the cotyledon = plumule+ radical The second stage is the emergence of the radicle and then the plumule from the cotyledon. The third stage: the emergence of green leaves  PARTS OF A FLOWERING PLANT The plant body of an angiosperm or a flowering plant primarily consists of an axis, which is differentiated into: Root system Shoot system MORPHOLOGY OF ROOT The root is a non-green, non- photosynthetic, cylindrical, descending part of the plant that develops from the radicle of seed. Positively geotropic and hydrotropic that normally grows downwards into the soil.  Characteristics of the Root It does not bear nodes and internodes. It does not bear leaves and buds. It is non-green. A functional root is covered at the tip by a root cap. Near the tip, the root bear unicellular tubular root hairs. Endogenous in Origin: Root branches develop from the interior (usually pericycle) of the parent root. A root is neutral or negatively phototropic, and positively hydrotropic. The geotropic response is also positive for the main root.  THE REGIONS OF THE ROOT A typical root possesses five parts or regions, however, there is no definite demarcation. Root Cap Meristematic Region Region of Elongation Region of Root Hairs Region of Maturity  Root Cap It is a cap-like structure present at the tip of root. The cells of the root cap secrete mucilage, which lubricates the passage of the root through the soil and help in easy penetration through the hard soil. The cells of the root cap also possess starch grains, which are believed to be responsible for the perception of gravity. The root cap also protects root meristem from friction between root and the soil particles  Meristematic Region It is one to a few millimeters in length and lies partly within and partly beyond the root cap. The cells of this zone divide actively and add new cells to the root and root cap. Root meristem keeps on adding new cells and replacing the worn-out cells.  Region or Zone of Elongation It lies behind the meristematic zone and is about 4-8 mm in length. The cells of this region are newly formed cells, which lose the power of division. They elongate rapidly and bring about an increase in the length of the root. They also possess the power of absorption of water and mineral salts from the soil.  Region of root hair It lies above the region of elongation and bears a cluster of very fi netubular outgrowths called root hairs. Root hairs are produced from the epiblema of the root. The root hairs increase the exposed surface of the root for absorption. This zone also represents the zone of differentiation or maturation because different types of primary tissues differentiate or mature in this region. As the root increases in length, the root hairs in older region get bruised and shed. New root hair appears in the younger part of the zone of elongation.  Region or Zone of Maturation This region forms a major part of the root and no change occurs in the cells of this region. It forms the permanent zone of the root and gives out lateral roots. The outermost layer of this region has thick-walled cells and hence, does not help in absorption of water from the soil.  ROOT SYSTEM The roots along with their branches, constitute the root system Root system can be classified according to the origin to: Root system Main tap root Adventitious roots Tap root develops from the (L. adventitious– radicle of the seed. It has a extraordinary) main primary root that Roots that develop from further gives rise to any part of the plant other secondary and tertiary than the radicle. branches MODIFICATIONS OF TAPROOT Fleshy taproot The taproots of some plants become swollen and fleshy due to the storage of food. Hypocotyl may also join the taproot in storing food. The secondary and tertiary roots remain thin and fibrous. Depending upon the shape, fleshy taproots are of the following types:  Fleshy / storage tap root (i) Conical (Cone-shaped): The primary root is broad at the base and tapers gradually towards apex like a cone. Many thin, threads like secondary roots arise all along the conical root, e.g., Carrot.  Fleshy / storage tap root (ii) Fusiform (spindle shaped) The primary root is spindle shaped. It is almost uniformly thick except at the base and apex where it tapers. The basal part of the root is derived from hypocotyl. The root also bears a reduced discoid stem and radicle leaves (leaves arising from roots or appear to arise from roots). Radish ( )..  Fleshy / storage tap root (iii) Napiform (pitcher-shaped) Globular or top-shaped and tapers abruptly towards the apex. Bears a reduced discoid stem and radicle leaves Basal part of the fleshy root is hypocotyl. For example, Turnip and beetroot. (iv) Tuberous roots (irregularly shaped) The primary root becomes thick and fleshy. No definite shape. four o’clock plant ( Mirabilis jalapa)  2. Pneumatophores or Respiratory Roots These are aerial roots or aerophores found in mangrove plants (plants growing in swamps near the seashores), e.g., (vern. ) The underground secondary and tertiary roots of the plants come out of swamp for exchange of gases. They bear small pores called lenticels or pneumatothodes near their tips. The remaining surface of pneumatophores is covered with cork and the proximal submerged part bears many short absorbing roots. Q:Pneumatophores are found in………. (1) The vegetation which is found in marshy and saline lake (2) The vegetation which is found in acidic soil (3) Xerophytes (4) Epiphytes 3. Nodulated taproots In some plants, secondary, tertiary and even primary roots bear many small irregular swellings called root nodules or tubercles. The root nodules contain millions of minute nitrogen fixing bacteria of the genus (Rhizobium spp.). These bacteria pick up free atmospheric nitrogen and convert it into nitrogenous organic compounds. This phenomenon is called nitrogen fixation. Plants belonging to family Leguminosae, such as pea, gram, groundnut, etc. Green manure: Legumes add nitrogenous compounds to the soil or increase the fertility of the soil as nitrogen fixing bacteria are in their root nodules, hence the roots are left over in the soil till the next harvest Q: Root nodule is a modified structure of ………….. (1) Adventitious root (2) Taproot (3) Fibrous root (4) Lateral root  MODIFICATIONS OF ADVENTITIOUS ROOT Modified for storage Modified for Modified for vital function additional support (i) Tuberous Root or Root (i) Prop or Pillar Roots (i) Assimilatory or Photosynthetic (ii) Fasciculated Roots (ii) Stilt Root or Brace Roots Roots (ii) Haustorial or Parasitic Roots (iii)Clinging or Climbing (iii) Hygroscopic or Epiphytic Roots Roots (iv) Floating Roots or Root Floats (v) Reproductive Roots  Storage adventitious roots Depending upon the shape and the swollen part, adventitious roots are of following types: (i) Tuberous Root or Root Tubers Such roots arise singly at the nodes of prostrate stem and are swollen without any definite shape. Also called root tubers, e.g., Sweet potato ( vern. ). Reproductive Roots: Roots do not bear buds but the root tubers of sweet potato bear adventitious buds which give rise to new plants, hence they are also known as reproductive roots  (ii) Fasciculated Roots These are swollen roots which arise in clusters or fascicles at the base of the stem, e.g.,. In , swollen are borne on the normal roots at intervals. The root system is often referred to as ‘crown’.  Roots Modified for Additional Support (i) Prop or Pillar Roots Pillar-like adventitious roots that arise from branches of the trees like banyan tree. Initially, these roots are aerial and hygroscopic. As the roots reach the soil, they become thick and pillar-like and start absorbing water and minerals. In old plants, the main trunk may die, but the crown of the tree is supported and nourished by the prop roots. Q: Prop roots are………… (1) Taproot (2) Adventitious root (3) Secondary root (4) All  Roots Modified for Additional Support (ii) Stilt Root or Brace Roots These are short and thick supporting roots which develop obliquely from the basal nodes of the stem. These roots penetrate down into the soil and give support to the plant, e.g., maize, sugarcane, sorghum , screw pine, etc. In , the stilt roots develop only from the lower surface of the obliquely bending stem. They bear much folded multiple caps at their tips.  Roots Modified for Additional Support (iii) Clinging or Climbing Roots These are non-absorptive adventitious roots found in some climbers. These may arise from the nodes, e.g., (Money Plant), or from internodes and both, e.g., Ivy. These roots either enter into crevices or cracks of the support or stick firmly to the support by secreting a cementing gummy substance. These help the climbers to climb up the support. Q: The plant which bears clinging roots is (1) Screw pine (2) Podostomen (3) Trapa (4) Orchid ROOTS MODIFIED FOR VITAL FUNCTIONS (i) Assimilatory or Photosynthetic Roots These are green roots, which are capable of photosynthesis, e.g., water chestnut. In some submerged roots are highly branched and green in colour to perform photosynthesis ROOTS MODIFIED FOR VITAL FUNCTIONS (ii) Haustorial or Parasitic Roots These roots occur in parasitic plants that are achlorophyllous. These roots absorb nourishment by establishing contact with the vascular tissue of the host plant. Hence, also called as sucking roots or suckers. e.g., (Dodder Plant) has non- green stem and bears scale leaves. Dodder plant is a total parasite on hosts like etc. and obtains both water and food from the host ROOTS MODIFIED FOR VITAL FUNCTIONS (iii) Hygroscopic or Epiphytic Roots These are adventitious roots found in some orchids. Orchids grow as epiphytes upon the trunks or branches of the trees. The epiphytes develop aerial roots which hang freely in the air. Roots of orchids are whitish in colour and are covered with a specialized spongy tissue called velamen. Velamen helps the roots in absorbing atmospheric moisture. Epiphyte: A plant that grows upon another plant only for shelter but is not a parasitem, e.g., orchid. ROOTS MODIFIED FOR VITAL FUNCTIONS (iv) Floating Roots or Root Floats These are inflated buoyant roots, spongy in texture due to abundant aerenchyma, arising at the nodes of some aquatic plants like. These roots grow out of water and keep the plant afl oat. ROOTS MODIFIED FOR VITAL FUNCTIONS (v) Reproductive Roots Some fleshy adventitious roots develop adventitious buds. Adventitious buds can grow into new plants under favorable conditions. Such roots are called reproductive roots. Sweet potato, etc.  FUNCTIONS OF ROOTS Roots perform two types of functions primary and secondary. A. Primary or Main Functions (Performed by all the roots) 1- Anchorage: The roots fix the plant in the soil firmly and support the aerial shoot system. 2- Absorption: The roots absorb water and mineral from the soil. The absorbed water and minerals are translocated to the stem through the xylem of the root. 3- Synthesis of plant growth regulators. 4- Prevention of soil erosion: Roots hold the soil particles firmly and prevent the soil from erosion.  Root secondary functions B. Secondary or Accessary Functions: The secondary functions are specialized functions and are performed only by those roots which are modified accordingly. 1- Storage of food: Some roots store food and become fl eshy, e.g., carrot, radish, , , sweet potato, etc. 2- Additional support: Some roots like prop roots and stilt roots provide additional support to the plant such as Maize. 3- Climbing: Some weak stemmed plants climb up a support with the help of clinging roots, e.g., (money plant), etc  Root secondary functions 4- Nitrogen fixation: The roots of some leguminous plants ( pea, gram, groundnut, etc.) contain nitrogen-fixing bacteria in their nodules. These bacteria fi x free atmospheric nitrogen. Thus, enrich the soil by adding nitrogen compounds. 5- Breathing: Respiratory roots or pneumatophores of mangrove plants have lenticels that help in exchange of gases. 6- Moisture absorption and retention: Hygroscopic roots of some orchids absorb moisture directly from the air. 7- Absorption of food: In parasitic plants, spine-like adventitious roots penetrate the host and obtain food and water from the latter. 8- Assimilation: The green roots of , water chestnut etc., carry out photosynthesis. 9- Floating: The roots of some aquatic plants store air and function as floats. 10- Balancing: Cluster of adventitious roots arising in free floating aquatic plants (e.g., etc.) helps in balancing the plants over water, surface. 11- Reproduction: The roots of some plants have adventitious buds (e.g., sweet potato) which help in reproduction. Rootless Plants: Submerged aquatic plants like do not possess roots. They absorb water and minerals directly from the surfaces of stem and leaves.  Stem morphology Stem: It is the main structural axes of vascular plants, it supports leaves, flowers and fruits. It develops from the seed plumule Stem characteristics Stem develops from the plumule and epicotyl of the embryo. It is generally an aerial and ascending part of the plant axis. Its apex bears a terminal bud for growth in length. It bears nodes and internodes. The stem nodes bear leaves. The young stem is green and is thus photosynthetic. In the mature state, it bears flowers and fruits. Stem branches and leaves develop exogenously. Hair, if present, is generally multicellular. Stem is positively phototropic and negatively geotropic. Q: Lateral organs of the stem are…… (1) Endogenous in origin (2) Exogenous in origin (3) Both (4) None of the above  Stem primary function Stem bears leaves, flowers and fruits. It conducts water and minerals from the roots to the leaves, flowers, and fruits. It also transports food, manufactured by the leaves to the roots, fruits and other storage organs of the plant. It adds new cells, tissues, and organs, which are required for the continued functioning of the plant because of the presence of terminal bud.  Stem secondary functions A large number of plants store food and water in their underground stems like rhizomes of ginger, corms (colocasia ) and tubers (e.g., potato). The stem of sugarcane which stores sugar in it. The stems of several succulent plants (e.g., ) store water. The underground stems such as rhizomes, corms, tubers, etc. perform the function of perennation (tiding over unfavourable growing period). In many plants, stems serve as a means of vegetative propagation as in the case of runner (e.g., grass), stolons (e.g., strawberry), offsets and underground stems (e.g., mint, Potato, etc.). Q: Which of the following is an underground stem? (1) Ginger (2) Sweet potato (3) Radish (4) Turnip  The stems of some weak-stemmed plants may be modified into tendrils (e.g., , Grapevine, etc.), thorns (e.g., ) and hooks (e.g., ) to help them in climbing. The stem of some plants is modified into thorns ( etc.), phylloclades (e.g.,) and cladodes (e.g., ) to reduce transpiration. The stem thorns as in etc., act as organs of defence and protect the plant from browsing animals. The stem in younger state and when modified into phylloclades (e.g., optunia) and cladodes (Rascus and asparagus), performs the function of photosynthesis. The stem when modified into a flower performs the function of sexual reproduction.