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In this article we will discuss about Stem of a Plant:- 1. Stem Surface 2. Forms of Stem 3. Modifications of Underground Stem 4. Some Other Stem Modifications.
Stem Surface:
1. Glabrous:
Smooth.
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2. Glaucous:
Shining and smooth.
3. Pubescent:
Covered with fine silky hair.
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4. Tomentose:
Covered with coarse wooly hair.
5. Prickly or spinose:
Covered with prickles or spines.
Forms of Stem:
(A) Creepers:
Weak herbaceous plants which cannot support themselves and run along the ground are called creepers.
They are rooted only at the nodes and are of following types:
1. Runner:
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A prostrate, slender stem with long internodes. They creep on the ground and form roots at the nodes, e.g., Oxalis, Fragaria vesca, etc.
2. Stolon:
Short branched runners are called stolons. Stolon originates laterally from the base of stem and runs horizontally, e.g., Passiflora, Colocasia, etc.
3. Sucker:
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It also develops laterally like stolon but grows obliquely upwards and bears leaves, e.g., Mentha (mint), Banana, etc.
4. Offset:
A short, thickened, prostrate branch like runner but developing tuft of leaves and clusters of roots below, e.g., Eichhornia, Pistia, etc.
(B) Trailers:
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Weak, thin, long shoots lying prostrate on the ground but lacking roots at the node are called trailers.
Trailers are of following types:
1. Diffuse:
Branches spreading in all directions, e.g., Boerhaavia diffusa, Senebiera etc.
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2. Decumbent:
Bulk of shoot lying on the ground with only tips of the branches being erect, e.g., Tridex.
3. Procumbent:
When shoot lie prostrate on the ground, e.g., Convolvulus etc.
(C) Twinners:
Plants ascending by coiling on the support without any special device on the latter, e.g. Clitorm ternatea.
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(D) Climbers:
Weak-stemed plants, ascending on the support by means of some special modifications. These are categorized into following:
1. Root climber:
Climb by aerial adventitious roots, e.g., Piper betel, Pothos, etc.
2. Tendril climber:
Climb by means of tendril, e.g., Vitis vinifera, Lathyrus aphaca, etc.
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3. Hook climber:
Climb by means of pointed, curved hooks, e.g., Bougainvillea.
4. Leaf climber:
Weak stem, climbing by means of petiole or leaf tips, e.g., Clematis.
5. Adhesive disc climber:
Climb by fixing the adhesive disc formed at the tip of the climbers, e.g., Ampelopsis.
6. Lianas:
Thick woody, perennial climbers, twinning round the big trees are called lianas, e.g., Hiptage.
Modifications of Underground Stem:
1. Rhizome:
Thick, prostrate, creeping stem running horizontally under the soil surface. It bears internodes, nodes and the scaly leaves on the nodes, e.g., Zingiber officinale, Nymphaea, etc.
2. Tuber:
Thick swollen end of the underground branches of stem. It bears eyes or buds, e.g., Solanum tuberosum (potato), Cyperus esculentus.
3. Bulb:
Underground modified shoot with many fleshy and scaly leaves. Terminal as well as axillary buds are present, e.g., Allium cepa.
4. Corm: Solid, round, bulb – like, fleshy underground stem usually covered with membranous scales, e.g. Colchicum, Crocus etc.
Some Other Stem Modifications:
1. Phylloclade:
It is a flat, green leaf like modification of entire shoot. Leaves are either absent or scaly, or modified into the spines, e.g., Ruscus, Opuntia etc.
2. Cladode:
A phylloclade in which a branch of a single internode becomes leaf-like or flattened, e.g., Asparagus.
3. Thorn:
A pointed, woody, sharp branch developing in the axil of leaves is called thorn, e.g., Carissa carandas.
