Stem

                                                Stem

    The portion of the primary axis of plant plant which develops from which plumule is called main stem. The axis with leaves is called shoot.Stem has node and internodes. The part of stem from leave arise is  called node. the part of stem between two nodes is called ineternode.Stem shows positive geotrompism and is always try to grow upward.Some stem are under ground these stem are called underground stem. They are often thick and swollen with a larger amount if stored food. Underground stems resemble with roots.They always arise from the axils of leaves. There are different types of under ground stem. These are rhizome,corm,bulb and stem tuber. Different type of terms are used for plants. These terms are Herbaceous stem Soft and green stem that can be easily bent is called Herbaceous stem. 

         woody stem hard woody stem which cannot easily bent is called stem. fistular if the inter node of the plant  are hollow ,then the stem is called fistular. solid if stem is not hollow at inter node then it called solid. Joined the stem swollen at internode are called joined. Example stem of grasses. Cylindrical straight and round stem is called cylindrical. Example rose. Angular the stem with alternate ridges and furrows is called angular. Example ocimum. Flattened flat and plant like stem is called flattend. Example opuntia. Succulent  thick and fleshy stem is called succulent. Example euphorbia. Hairy the stem having hair on is surface is called hairy. Example sunflower.Spiny With spines or thorns on the surface is called spiny. Example Acacia (kikar).Prickly Stem with prickles on the surface .Example rose.Some plants have weak and slender stem.Such plant cannot grow erect.Therefore they adopt different method to get  support. They climb the support. They develop different structures for climbing. These structures help them to attach with different supports.

Types of stem 

   Different types of plant stem are present.Stems have following forms Aerial stems and under ground stem  Aerial stem The stem which grows above the ground in the exposed air is called aerial stem.It may be Reduced aerial stem In this case stem is very reduced and present in the form of green structure above the thick roots.These stem ate so small that the leaves appear to be arised from root directly . Example stem of radish turnip etc. Erect  stem In this case stem is thick and strong It grow upward. Such  stems are present in trees Weak stem these stem are much weak. They are unable to grow erect. Therefore they become climber or spread on the ground. Plants are divided into different group on the basis on structure of their weak stem.Climbing plants or climber these plants have weak and slender stem. Such stem cannot grow erect. Therefore, they grow adopt different method to get support.They develop different structures for climbing. These structure help to attach with different support. The plants whose stem are twin or coil around some support are 

called twiners.They do not have any special organ. They have long slender stem with long inter nodes.Thus their long stem coils around host plant. The direction twining may be clock wise or anticlockwise Example Cuscuta. Tendril climber these plants develop long slender long tendrils for climbing up in the support . The tendril may be modified stem or leaves. It is very sensitive to support. As soon as it touch some support. It coil. Ex melons cucumber etc.Root climber These plants are attach to the support by means of small advantitious roots.These are arise form the sides of stem. such roots are very sensitive to touch . they twin around the support. They penetrate into gap in stem of host plant and firmly attach the plant with it. They also produce sticky fluid. It adhere the plant with host plant.Example pepper. Hook Climber these plant develop hooks to attach with support. The hooks are uncurved Example Bougainvillea. Leaf Climber  The leaves of some climber become elongated. They grip the support and help the plant to remain erect. Example is pitcher plant.

Under ground Stem  These are grow underground. They often thick and swollen with a large amount of stored food. They are formed by perennial herbs. Underground stem resemble with roots. But stem have node and inter node or scale leaves. They always arise from axils of leaves. Rhizome The elongated thick, horizontal,thick and fleshy underground stem.Store large amount of food. It has node and inter node.There are different form of of node and inter node.Straggling Rhizome  The elongated thick less branched rhizome which grows horizontally.Example grasses (typha).Monopodial Rhizome  they are arranged like racemose. They have single axis which give rise to lateral branch.They are present in many wood sorrel. Sobole Rhizome are long slender and has long inter node found in grasses. Corm Thick solid rounded under ground stem with few inter node is called corm.It covered with number of loose of sheathing scale leaf. One or more bud is present in axil of each leaf. Each bud form new corm. Example Colocasia. Bulb specialized much reduced short under ground stem composed of broadly conical disc is called bulb.Large fleshy leaves are burn on the surface. These leaves are small scale leaf like onion.Bulb  different form like Tunicated bulb, Scaly bulb.

Function of stem

•  Stem  bear leaves  flower  and fruits. Stem expose to them to sunlight.
•  Stem conduct water and dissolved substances to different part of plant
•  In some cases they serve the function of leaves like Phylloclades and cladodes.
•  Succulents     are   used  storing   of     water   in   arid   areas. In  some   cases   stem           are  used  for   climbing  like   tendrils.                                                         
•   Stems in the form of thorns protect the plants from grazing animals.
•   Stems   are    used   for   vegetative    propagation.