Plant stem
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The document defines the stem as the upward-growing organ of the plant that supports leaves, branches, and flowers, highlighting its characteristics, classifications into normal and modified stems, and various examples. It details the functions of the stem, including conducting nutrients and water, storing food, photosynthesis, and aiding in vegetative propagation. Additionally, it discusses specific types of normal stems (strong and weak) and modified stems, elaborating on their characteristics and functions.
Plant 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 A. Strong or Erect Stem: It has five more classification as following- a. Culm e.g. Bamboo b. Caudex e.g. Coconut, Palm c. Excurrent e.g. Jhau d. Deliquescent e.g. Mango e. 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 I. Creeping e.g.Durba II. 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. A. Underground modified stem B. Sub-aerial modified stem C. Aerial modified stem Underground Modified Stem I. Rhizome: A thickened horizontal under ground stem provided with distinct nodes and internodes. Example: Ginger,Turmaric II. Tuber : A thicked short underground branch of the stem serving as a storage organ containing reserve food. Example : Potato
- 8. Continued…….
- 9. Continued….
- 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.
- 11. Continued….
- 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 I. Tendril : This is a thin, leafless branch used as a climbling organ by climbers. Example : Passion Flower II. Thorn: It is a pointed branch; may be a modification of an axillary bud or a terminal bud. Example: Lemon III. 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 IV. Phylloclade: This is a green, flattened stem consisting of nodes and internodes. Example: Pear V. Bulbil : It is the modification of a vegetative bud or of a floral bud. Example: Oxalis
- 14. Continued….
- 15. Functions of Stem General Function 1. A stem bears leaves, branches, flowers and fruits. 2. It conducts water and mineral nutrients from root to the leaves and living tissues 3. It conducts food materials from leaves to the roots, living tissues and storage organs. Special Functions 1. Stem stores food materials e.g. Potato, Carrot. 2. Green stem takes part in photosynthesis and manufactures food material 3. It takes parts in vegetative propagation or reproduction through axillary bud e.g. Garlic, Onion 4. It develops tendril to climb e.g. Cucurbit 5. It takes part in defense mechanisms by developing thorn e.g.Bel.
- 16. End