2011

 stem may be defined as something that bears leaves.  But this definition is too simplistic; it needs to be expanded  From where does a stem come?  What part of the seed produces it?  When one dissects a seed, it is found to bear a seed coat or two and, within the seed coat, an embryo.  The embryo consists of cotyledons (the seed leaves, which are food sources),

 a radicle (which grows downward upon germination to produce the root),  and a plumule (which grows upward to produce the stem and leaves).  The cotyledons are attached to the plumule.  The seedling thus has two parts:  the epicotyl (that part above the cotyledons) and  the hypocotyl (that part below the cotyledons).  Thus, a stem can be defined as that part of a plant above the hypocotyl.

 The stem is the ascending portion of the axis of the plant,  develop directly from the plumule,  and bears leaves, branches and flower.  When young its is normally green in color.  The growing apex is covered over and protected by a number of tiny leaves

 It branches exogenously and  is provided with nodes and internodes which may not be distinct in all cases.  Leaves and branches normally develop from the nodes.  When the stem or branches end in a vegetative bud it continuous to grow upwards or side ways.  If however, it ends in a floral bud, the growth ceases.

 There is a variety of stem structures adapted to perform diverse functions. 1. aerial or 2. underground. Aerial:  may be erect, rigid and strong, holding themselves in an upright position,  while there are some too weak to support themselves in such position.  They either trail on the ground or climb neighboring plants and other objects.

Underground Stem:  Some stems remain permanently underground and  from there, periodically give off aerial shoots under favorable conditions.  Such stems are meant for food storage and perennation.

 The unbranched and stout stem, marked with scars of fallen leaves is called caudex as in palms.  Jointed stem with solid nodes and hollow internode is called culm, Eg. Bamboo  some herbaceous plants, particularly monocotyledons have no aerial stem.  The underground stem in them produce as erect unbranched aerial shoot bearing either a single flower or cluster of flowers such a flowering shoot is called scape.  Eg. Tuberose, onion, aroids banana etc.

 Three kinds: 1. Trailers:  those plants whose thin and long or short branches trail on the ground, with or without rooting at node.  Such plants like prostrate on the ground they are said to be prostrate or procumbent.  When the branches of such plants, after trailing for some distance, tend to rise at their apex they are said to be decumbent  Eg. Tridax.

 when the plants are much branched  the branches spread out on the ground in all directions, they are said to be diffused  eg. Boerhavia.

2: Creepers  Week-stem plants with their long or short branching creeping along the ground  rooting at the node are said to be creepers,  a creeping stems may be runnner, stolon, offset or sucker according to its varied nature.

 Plants that attach themselves to any neighboring object,  mean of some special devices, and  climb it to a long or short distance.  Eg pea, vine, passion flower, gourd etc etc.

 Gymnosperms are entirely woody,  while both woody and herbaceous forms occur in angiosperms.  Angiosperms include both monocot and dicot.  These differences create a need for several descriptions of stem anatomy.

What are the differences in cross section view between dicot and monocot stem?

 What are the underground modification of stems?  What are the aerial modification of stem?  What are the functions of stems?

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