shoot morphology Description with examples.pptx

Shoot morphology Description

1. Chapter 3 The stem and stem branching

2. The stem develop from the plumule of the germinating seed. Normally it is the aerial part of the plant body. The stem with it's branches, leaves, buds, flower and appendages is known as shoot system. The stem shows the differentiation of nodes and internodes. The place where the leaf develops on the stem is called the node. The portion of the stem between two successive nodes is called the internode. The stem

3. Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo. It is generally erect and grows away from the soil towards light. The growing apex of stem bears a terminal bud for growth in length. In flowering plants, stem is differentiated into nodes and internodes. The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region). The young stem is green and photosynthetic. Hair, if present, are generally multicellular. In mature plants, stem and its branches bear flowers and fruits. Characteristics of the stem

4. Diverse forms of stem

5. Aerial stem Aerial stem are above ground stem which may be erect, rigid and strong, holding themselves in an upright position. In contrast, others may be too weak to support themselves in upright position hence they either trail on ground or climb on neighbouring plants and other objects. Erect or strong stem Caudex: It is unbranched, erect, cylindrical stout stem and marked with scars of fallen leaves as in palms. Eg : - cocos nucifera Culm: - Stem is jointed with solid nodes & hollow internodes clasped by leaf sheaths. E.g. Bamboo ( Gramineae ).

6. Excurrent The main axis shows continuous growth and the lateral branches gradually becoming shorter towards the apex which gives a conical appearance to the trees. Example: Polyalthia longifolia , Casuarina . Decurrent The growth of lateral branch is more vigorous than that of main axis. The tree has a rounded or spreading appearance. E.g. Mangifera indica , Azadirachta indica , Tamarindus indicus ,

7. Scape:- In some monocotyledons there is no aerial stem instead there are aerial shoot (Branch) which bear flowers. Eg :- Onion and aroids Aerial stem cont...

8. Weak stem Weak stems are of three kinds Trailers Creepers Climbers Trailers: Shoots made up of thin and long or short branches which trail along the soil surface with or without rooting at the nodes. There three types of trailers; Prostrate – trailers which lie prostrate on the ground, e.g Oxalis spp Decumbent – trailers whose branches after trailing for some distances tend rise at the apex Diffuse – trailers which produce several branches which spread out on ground in all directions

9. Creepers - Weak shoots having long or short branches creeping along the soil surface and produce roots at the nodes. There four types of creepers; Runners e.g. Cynodon dactylon Stolon, Offset and Sucker - the main stem grow in the soil but branches develop from nodes above the soil e.g. Pineapple, Climbers - plants that attach themselves to any neighboring object, often by special device, e.g pea, passion flower, guard, vine, etc.

10. Parasites – plants which grow upon other living plants or animals and absorb organic nutrients from the host by their sucking root Haustoria . There four categories of parasitic plants Total stem parasites – (Dodder (Cascuta spp ) Partial stem parasites – Total root parasites – parasites on plant roots Partial root parasite – Witch weed ( Striga spp ) Special type of plants

11. P lants that grow on other plants but do not suck or absorb nutrients from them. They develop three types of roots Clinging roots – grow into cracks and crevices in the barks of the supporting plant and fix the epiphyte in proper position for anchorage. Absorbing roots – develop from clinging roots and project into the humus from which they draw nutrients Hanging roots- they have outer covering of a special absorptive tissue called velamen which usually consist of 4-5 layers of oblong polygonal cells. The cells are dead containing only air and water. They play role to absorb moistures from the surroundings. Epiphytes

12. Stems develop underground and lodge permanently lying dormant, defoliated for some time and then sprouting aerial shoots annually when conditions are favorable. They are always thick and fleshy, containing a heavy deposit of food. They differ from roots in the following aspects; Have nodes and internodes Have scale leaves Have buds (axillary and terminal) Underground stem modification

13. Rhizomes- are underground stems that grow near the soil surface. They typically have short internodes and scale leaves, and produce roots along their lower surface. They store food for renewing growth of the shoot after periods of stress. E.g. ginger

14. are swollen regions of stems that store food for subsequent growth. It is a stem because it has many nodes called eyes with spaces between eyes known as internodes. Tubers develop at the end of swollen underground stem structures like rhizomes. The eyes of tubers are really axillary buds which contain several small buds at each site. These buds can expand to form shoots which grow on to make whole plants. The potato is an example. Tuber

15. Are rosette stems surrounded by fleshy leaves that store nutrients. A bulb consists of a stem from which modified fleshy leaves develop. The fleshy leaves are circular and hollow; new leaves develop within the older leaves. Leaves are attached to the stem at nodes and spaces between nodes are called internodes. The presence of nodes and internodes means that the bulb is actually a modified stem. The papery covering is called a tunica. E.g. Onion, Garlic, Leak, Lilies etc Bulbs

16. Stem tendrils – thin, wire like, leafless, spirally coiled branch by which climbers attach themselves to neighbouring objects and climb. E.g. vine, passion flower. In passion flower, the axillary bud is modified into tendrils.

17. Thorn – T hey are hard often straight and pointed structures. They regarded as modified branches because they arise in the axil of a leaf or sometimes at the apex of a branch which is the normal position of a bud. Prickle and hooks - These developed only from cortex and epidermis and found at nodes or internodes. it helps in climbing. It is exogenous in origin. Eg . Rose, Smilax

18. F lattened or cylindrical stem or branch of unlimited growth. It consists of succession of nodes and internodes of long or short intervals. It is a characteristic of many xerophytes where leaves grow feebly, or fall off early or modified into spines to reduce evapotranspiration. The phylloclade takes over all the functions of the leaf, particularly photosynthesis, it also functions as storage tissue, retaining plenty of water and mucilage. Furthermore because of strong development of cuticle, it can reduce transpiration to a considerable extent eg ( Opuntia dillenii ) Phylloclade

19. It bears and support leaves, flowers and fruits. The various appendages borne on the stem are placed in such a fashion that they are able to carry out their functions most effectively. It conducts the water and minerals from roots to leaves and fruits. Stem bears flowers and fruits in position to facilitate the processes of pollination and fertilization. Every year it adds new cells, tissues and organs which are required for the continued functioning of the plants. Primary functions of Stem

20. Storage of food: In a large number of plants, the stems store food and water. Perennation: The underground stems help to tide over the unfavourable growing period Vegetative propagation: In a large number of plants, the stems are used for vegetative multiplication Photosyntheis : In some xerophytes, the stem becomes green and modified into leaf-like structures Protection against browsing As climbers: The stems may be modified into tendrils, hooks, thorns etc. to. Receptacle for floral organs: In a flower, the floral organs are borne on the thalamus. The thalamus is a modified stem which has condensed and overlapping nodes and internodes. Secondary function of the stem

21. Branching pattern is determined by the relative activity of apical meristems. The mode of arrangement of branches on a stem is known as branching. Stem Branching

22. Branches are produced laterally, that is from the sides of the main stem. There are two kinds of lateral branching, Racemose/indefinite or monopodial and cymose or definite. Lateral branching Racemose The growth of the stem is indefinite or indeterminate. It continues to grow indefinitely by the terminal bud and give off branches laterally in acropetal succession. I.e. lower branches are older and longer than the upper ones. It is also called monopodial type because there is single continuous axis. The plants canopy takes a conical shape.

23. Growth of the main stem is definite (determinate). i.e. the terminal bud does not continue to grow indefinitely, but the stem produce one or more lower branches which grow vigorously than the terminal bud. The process may be repeated more and more resulting to a dome shaped canopy. Cymose lateral branching is categorized into three; Uniparous or monochasial cyme Biparous cyme or dichasial Multiparous cyme Cymose

24. Uniparous or Monochasial When single lateral branch is produced at a time. It is further divided into two distinct types Helicoid- Lateral branches are produced on one side only e.g. Saraca . Scorpoid - Successive lateral branches are produced on alternate side e.g. Grape vine. Biparous or Dichasial When two lateral branches are produced at a time. e.g. Mirabilis, Viscum , Silene , Carissa carandas . Multiparous or Polychasial When more than two branches are produced at a time. e.g. Euphorbia.

25. Dichotomous Branching: It is common only in lower plants (cryptogams) where the growing point bifurcates or divides into two equally vigorous parts. The branches behave in the same manner

26. Functions of stem Bear leaves and expose them for proper functioning Bear flowers and expose them for efficient pollination Support branches which push leaves and flowers further for more exposure Conduction of water and minerals and manufactured photosynthetic products Storage site in some plants Manufacture of food in some plants