248 ELEMENTARY STUDIES IN BOTANY 



some other way than as foliage. A stem and its leaves taken 

 together constitute the shoot (as contrasted with the root), 

 and since both must be considered in connection with the 

 subterranean habit, the shoot, rather than the stem alone, 

 will be discussed. A subterranean shoot may be distin- 

 guished from a root not only by the leaves (or structures 

 representing leaves) it bears, but also by its internal struct- 

 ure, which is very different from that of a root, as will appear 

 in the next chapter. In general, the subterranean shoot 



FIG. 216. Rootstock of Solomon's seal, showing terminal bud, the base of this year's 

 aerial branch, and scars of the branches of three preceding years. After GRAY. 



is used for food storage, and the three following kinds are 

 the most common. 



(1) Rootstock. This is probably the most common form 

 of subterranean stem (also called a rhizome). It is usually 

 horizontal, more or less elongated, and usually much 

 thickened for food storage (Fig. 214). It advances through 

 the soil year after year, often branching, sending out roots 

 beneath and leaf-bearing branches into the air. As it con- 

 tinues to grow at the apex, it gradually dies behind, thus 

 isolating branches in the case of branching rootstocks. It 

 is a very efficient method for the spreading of plants and is 

 extensively used by grasses in covering areas and forming 

 turf. The persistent continuance of some weeds, especially 

 certain grasses and sedges, that infest lawns and meadows, 

 is due to this habit (Fig. 215). It is impossible to remove 

 from the soil all of the indefinitely branching rootstocks, 



