ITS SUBTERRANEAN MODIFICATIONS. 



109 



roots. The nature of the Potato is also well shown by an acci- 

 dental case (Fig, 140), in which some of the buds or branches 

 above ground showed a strong tendency to develope in the form of 

 tubers. By heaping the soil around the stems, the number of tu- 

 beriferous branches is increased. The Jerusalem Artichoke affords 

 a good illustration of the tuber (Fig. 139). A tuber of a rounded 

 form, and with few buds, is nearly the same as 



176. A Corm (Cormus), or Solid Bulb. This is a fleshy sub- 

 terranean stem, of a round or oval figure, and a uniform, com- 

 pact texture ; as in the Arum triphyllum or Indian Turnip (Fig. 

 144), the Colchicum, the Crocus (Fig. 148), the Cyclamen,* &c. 

 It may be compared to the globular stem of a Melon-Cactus, like 

 which it has no power of elongation ; or it may be viewed as a 

 tuber or rhizoma reduced to the greatest simplicity, developing one 

 or more buds from its summit, and emitting roots from its base. 

 Corms are often termed solid bulbs; and, indeed, they are only a 



* The broad and flattened corm of Cyclamen arises from the dilatation of 

 the first internode of the stem, that which preexists in the embryo below the 

 cotyledons or seed-leaves. In many plants, this internode, or that immedi- 

 ately above the cotyledons, enlarges with the root. This occurs in the Tur- 

 nip, Radish, Beet, &c.; where the root thus produced, or at least the upper 

 part of it, presents the structure of the stem. 



FIG. 139. Base of the stem of the Jerusalem Artichoke (Helianthus tuberosus), showing the 

 nature of the tubers. 



FIG. 140. A monstrous branch or bud of the Potato, showing a transition to the tuber. 

 (From the Gardener's Chronicle.) 



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