Plant stem

In Plant physiology stem act as one of the main characteristics which bear leaves,flowers,fruits and many other activities will done through the stem.

1. Stem Prepared BY— ROKSANA AFTAB RUHI DEPARTMENT OF AGRICULTURE NOAKHALI SCIENCE AND TECHNOLOGY UNIVERSITY NOAKHALI,CHITTAGONG,BANGLADESH.

2. Definition of Stem Stem is the ascending organ of the plant developing from direct prolongation of the plumule . It normally bears leaves, branches, flowers.

3. Characteristics of the Stem It develops from the plumule and grows upward i.e towards light and remains above the ground. At young stage it becomes green in colour . It bears node, internode, terminal and axillary buds. It produces sexual reproductive parts and parts of the stem may be used for vegetative propagation.

4. Classification of Stem Mainly Two Classes- 1)Normal Stem 2)Modified Stem Normal stem is classified into two types- A)Strong or Erect Stem(stout and stand upright) B)Weak Stem(soft and cannot stand upright)

5. Continued….Normal Stem Strong or Erect Stem: It has five more classification as following- Culm e.g. Bamboo Caudex e.g. Coconut, Palm Excurrent e.g. Jhau Deliquescent e.g. Mango Scape e.g. Onion, American Aloe.(A scape is a leafless flowering stem)

6. Continued…Normal Stem B . Weak Stem: It has classified into the following types- 1) Prostrate: Remain flat on the ground Creeping e.g.Durba Trailing e.g. Tridax Procumbent e.g. Nunia shak Flat on the ground but tip erect e.g. Tridax Diffuse e.g. Punarnava 2) Climbing : Supported by climbing e.g. Morning glory Stem climber e.g. Madhabilata Root climber e.g. Pan Tendril climber e.g. cucurbit Spine climber e.g. Baghanbhilash

7. Continued…Modified Stem Modified stem is also called special type of stem. Underground modified stem Sub-aerial modified stem Aerial modified stem Underground Modified Stem Rhizome: A thickened horizontal under ground stem provided with distinct nodes and internodes. Example: Ginger,Turmaric Tuber : A thicked short underground branch of the stem serving as a storage organ containing reserve food. Example : Potato

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10. Continued… iii .Bulb : An underground bud covered by fleshy scales .Example: Onion,Garlic iv .Corn : Fleshy underground stem having brown scaly leaves growing in the vertical direction. Example: Taro,Colocasia .

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12. Continued…. Sub-aerial Modified Stem I. Runner : This is a slender prostrate shoot or branch with long internodes Example: Oxalis II. Stolon: It produces adventitious roots .Example: Taro III. Offset : This is more or less thickened, horizontal branch,originates in the axil of a leaf. Example : Water Hyacinth IV. Sucker : This is a lateral branch developing from the underground part of the stem. Example: Banana.

13. Continued….. Aerial Modified Stem Tendril : This is a thin, leafless branch used as a climbling organ by climbers. Example : Passion Flower Thorn: It is a pointed branch; may be a modification of an axillary bud or a terminal bud. Example: Lemon Cladode : In some plants one or more short, green cylindrical or sometimes flattened branches of limited growth developed from the node of the stem. Example: Asparagus Phylloclade: This is a green, flattened stem consisting of nodes and internodes. Example: Pear Bulbil : It is the modification of a vegetative bud or of a floral bud. Example: Oxalis

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15. Functions of Stem General Function A stem bears leaves, branches, flowers and fruits. It conducts water and mineral nutrients from root to the leaves and living tissues It conducts food materials from leaves to the roots, living tissues and storage organs. Special Functions Stem stores food materials e.g. Potato, Carrot. Green stem takes part in photosynthesis and manufactures food material It takes parts in vegetative propagation or reproduction through axillary bud e.g. Garlic, Onion It develops tendril to climb e.g. Cucurbit It takes part in defense mechanisms by developing thorn e.g.Bel .

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