Short essay on Kinds and Functions of the Stem

The stem is the ascending portion of the plant body developing from the plumule during germination.

The stem with the lateral appendages constitute the shoot system. The skeleton of the shoot is formed by the stem.

It is the aerial part of the plant, positively phototropic, growing vertically up, while its branches grow horizontally. The young normal stem is generally green. The stem bears leaves and flowers.

Functions of the stem:

1. Conduction: The water and mineral salts which are absorbed by the root are conducted to the leaf by the stem. Similarly, it conducts Stem-apex prepared food martial from the leaf to the growing regions and storage organs of the plant body.

2. Support: It provides requisite support to the plant. It supports the spread out branches and leaves.

3. Food manufacture: The green coloration of young stem is due to presence 0 chlorophyll which manufactures food material for the plant.

Kinds of stem

There are different kinds of stem to perform diverse functions. They may be aerial or underground. Aerial stems may be erect, rigid or strong in order to allow the plan to stand in an upright position. The other category of stem is weak. The weak stem either trail on the ground or climb on neighboring plants or objects.

A. Strong stems:

The strong stem may be of different types. It may be caudex, when it is un branched, erect, cylindrical, stout and marked with scars of fallen leaves, e.g., palms. Culm type stem with solid nodes and hollow internodes is found in bamboo.

Certain plants remain un branched with a flowering shoot developing from the underground stem. Such plants possess a cluster of leaves only at the base and the remainder of the stem remains leafless. Such special aerial stems are called scape.

B. Weak stems:

Plants with weak stem require a support for growth or else they trail on the ground. It is of the following types.

1. Trailing:

It grows on the surface of the ground without rooting at the nodes. It may be procumbent lying prostrate on the ground (e.g., Evolvulus, or decumbent when after growing on the surface of the ground for some distance, the growing apex rises up (e.g., Tridax, Lindenbergia, Trailing plants do not try to climb upon any support. A trailing plant is said to be diffuse, when the stem is much branched and the branches spread out on the ground in all directions (e.g., Boerhaavia).

2. Creeping:

When the weak plants produce adventitious roots at their nodes and creep on the ground it is said by creeping stem. These do not to climb upon any support. These are said to be creepers, e.g., Cynodon dactyl on, and Centella asiatica.

3. Climbing:

These are weak stems which grow on support. Usually, they grow up and expose their leaves to sunlight. There are different types of climbers such as: (i) twines; (ii) tendril climbers (iii) root climbers (iv) ramblers (v) adhesive climbers and (vi) lianas.

(i) Twiners:

These are weak stems which twine round the support. The growing apex circle round the support and such a growth movement is called circumnutating. Normally the growing apex of the stem coils clockwise or anti clockwise around the support, (dextrose or sinislrorse respectively) as found in Dioscorea or Clitoria.

(ii) Tendril Climbers:

These make use of specialized climbing organs called tendrils which are soft, wiry and coil like-structures. Tendrils are sensitive and capable of growing spirally around the support when comes in contact with the latter. In many cases it is the aerial part of the stem modified to form tendrils, e.g., Cucurbita.

(iii) Root climbers:

The weak stem can climb up by ad- ventitious roots produced at the nodes as in Piper betel which act as holdfast fastening the stem to the support.

(iv) Ramblers or scramblers and hook climbers:

Plants like rose, cane, Artabotrys and Lantana are having weak stems which do not actually climb, but grow over other bushes. They have superficial outgrowths such as thorns, prickles and curved hooks, etc. for climbing.

(v) Adhesive climbers:

In some Ficus species, adhesive discs grow from s climbing roots to form carpet like growth covering steep walls. By means of these discs the weak stems adhere to flat walls and grow up.

(vi) Lianas:

These plants grow like ordinary twiners over tall trees. These are perennial woody climbers. Once they reach the upmost part of the supporting tree and their top leaves get sunlight, the weak stem becomes very strong, stout, and woody, e.g., Tinospora, species of Bauhinia and Ficus, etc.