STEMS
The stem is the ascending axis of the plant, which usually bears the leaves, flowers, and fruit. The points on the stem to which the leaves are fastened are called the nodes; and the portions of stem between the nodes are called the internodes. The angle formed by the upper side of the leaf and the stem is called the axil.
Stems aboveground are classed as—
erect, when growing upright;
procumbent, when lying on the ground without rooting;
decumbent, when lying on the ground with the tip ascending;
diffuse, when loosely spreading;
creeping, when growing on the ground and rooting.
Stems underground are classed as rhizomes (or rootstocks) tubers, corms, and bulbs, the forms passing into one another by gradations.
A rhizome, or rootstock, is a horizontal underground stem. It is sometimes thick, fleshy, or woody, as in the iris;
a tuber is a short, much thickened rootstock, having eyes or buds of which the potato is an example;
a corm is a depressed and rounded, solid rootstock; it may be called a solid bulb; the garden cyclamen is an example;
a bulb is a leaf-bud, commonly underground, with fleshy scales or coats; the lily is an example.