EOOTSTOCKS AND TUBKRS. 



107 



nearly in contact (Fig. 167). In the very short and slow-growing 

 rootstock of Trillium (Fig. 169), the base of the leaf-bearing and 

 flowering stem of the season surrounds and coYers the terminal bud. 

 In our common Dentaria or Toothwort, and in Ilydrophyllum, the 

 base of this annual stalk or of the leafstalks partakes in the thicken- 

 ing, and persists as a part of the rhizoma, in the form of fleshy scales 

 or tooth-shaped processes. In other scaly rootstocks, these persist- 

 ent bases of the leaves are thin, and more like bud-scales, and slowly 

 decay after a year or two. All such markings are vestiges of leaves, 

 &c., or the scars from which they have fallen or decayed away, and 

 indicate the nodes. They show that the body that bears them 

 belongs to the stem ; and not to the root, which is wholly leafless. 

 Root-stocks branch, just as other stems do, by the development of 

 lateral buds from the axils of their scales or leaves. They serve 

 as a reservoir of nourishing matter, for the maintenance of the an- 

 nual growth, in the same manner as do thickened roots (14o, 146). 

 When such subterranean stems are thickened at the apex only, they 

 produce 



189. A Tuber. This is usually formed by the enlargement of the 

 growing bud of a subterranean branch, and the deposition of starch, 



&c. in its tissue. This deposit serves for the nourishment of the 

 buds (eyes) which it involves, when they develop the following year. 

 The common Potato offers the most familiar example ; and it is 



FIG. 170. Base of tlie stem of the Jerusalem Artichoke (Helianthus tuberosus), with its 

 tubers. 



FIG. 171. A monstrous branch or bud of the Potato, above ground, showing a tiansition 



to the tuber, (From the Gardener's Chronicle.) 



