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.
Shining and smooth.
Covered with fine silky hair.
Covered with coarse wooly hair.
5. Prickly or spinose:
Covered with prickles or spines.
Forms of Stem:
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:
A prostrate, slender stem with long internodes. They creep on the ground and form roots at the nodes, e.g., Oxalis, Fragaria vesca, etc.
Short branched runners are called stolons. Stolon originates laterally from the base of stem and runs horizontally, e.g., Passiflora, Colocasia, etc.
It also develops laterally like stolon but grows obliquely upwards and bears leaves, e.g., Mentha (mint), Banana, etc.
A short, thickened, prostrate branch like runner but developing tuft of leaves and clusters of roots below, e.g., Eichhornia, Pistia, etc.
Weak, thin, long shoots lying prostrate on the ground but lacking roots at the node are called trailers.
Trailers are of following types:
Branches spreading in all directions, e.g., Boerhaavia diffusa, Senebiera etc.
Bulk of shoot lying on the ground with only tips of the branches being erect, e.g., Tridex.
When shoot lie prostrate on the ground, e.g., Convolvulus etc.
Plants ascending by coiling on the support without any special device on the latter, e.g. Clitorm ternatea.
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.
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.
Thick woody, perennial climbers, twinning round the big trees are called lianas, e.g., Hiptage.
Modifications of Underground Stem:
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.
Thick swollen end of the underground branches of stem. It bears eyes or buds, e.g., Solanum tuberosum (potato), Cyperus esculentus.
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:
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.
A phylloclade in which a branch of a single internode becomes leaf-like or flattened, e.g., Asparagus.
A pointed, woody, sharp branch developing in the axil of leaves is called thorn, e.g., Carissa carandas.