STEM AND BRANCHES. 



11 



by twining about some support ; prostrate, lying flat on the ground ; 

 trailing, running along over the surface of the ground or other plants, etc. 

 Thus far we have studied the stem as it ordinarily appears to us above 

 ground, but there are stems of vast importance which are wholly subter- 

 ranean and are commonly spoken of as roots. That of Solomon's-seal 

 (Fig. 15) will serve as an illustration of one form of such stems. Placed just 

 beneath the surface in a horizontal position, it appears as a thickened, fleshy, 

 root-like bod}', bearing numerous rootlets, a terminal scaly bud at its 

 anterior extremity, and sending up a flower-stem, behind which are scars 

 left by the falling away of previous ones. Each year a new joint is added, 

 while commonly the oldest one rots away ; hence the stern is slowly, year by 

 year, creeping forward. Such an underground stem is called a rhizome. 



Fig. 10.— Hyacinth bulb. 



Pig. 17. — Vertical section of a hyacinth bulb. 



Ehizomes present many different forms. They are simple or branched, 

 horizontal or ascending, fleshy, etc., and are perennial. Podophyllum, 

 sanguinaria, and iris are among our active medicinal plants which have 

 stems of this character. 



In general, rhizomes contain the more active princirjles of the plants, 

 and in the greatest proportion. As such plants store away a great amount 

 of nourishment in their fleshy stems for the succeeding year's needs, they 

 commonly make vigorous growth early in spring, and are mostly early 

 bloomers. 



Another common form of subterranean stem is the bulb *, that of tliq 

 hyacinth (Fig. 16) affording a good illustration. A vertical section (Fig. 17) 



