108 



THE STEM. 



very evident on inspection of the growing plant, that the tubers 

 belong to branches, and not to the roots. The nature of the potato 



is also well shown by an accidental case (Fig. 171), in 

 of the buds or branches above ground thickened and 

 manifested a strong tendency to develop in the form 

 of tubers. By heaping the soil around the stems, 

 the number of tuberiferous branches is increased. 

 The Jerusalem Artichoke also affords a familiar il- 

 lustration of the tuber (Fig. 170). A tuber of a 

 rounded form, and with few buds, or a rhizoma 

 somewhat shorter and thicker than that in Fig. 109, 

 effects a transition to 



190. A Corm {Cormus), or Solid Bulb. This is a 

 fleshy subterranean stem, of a rounded or oval figure 

 and a compact texture ; as in the Arum or Indian 

 Turnip (Fig. 175), the Colchicum, the Crocus (Fig. 

 180, 181, 182), the Cyclamen,* &c. Corms have 

 been termed solid bulbs. But the principal bulk of 

 a true bulb consists not of stem but of leaves. 



which 



* The flattened corm of Cyclamen originates from the dilatation of the radicle 

 itself. In the Turnip, Beet, and Radish (Fig. 138), this also enlarges with the 

 proper root, the upper part of which accordingly partakes of the nature of the stem. 



FIG. 172. The Bcaly bulb of a Lily. 173. A vertical section of the same, forming the an- 

 nual stalls. 174 Axillary bulblets of Lilium bulbiferum. 175. Corm of Arum triphy Hum. 



FIG. 176. A radical leaf of the White Lily, with its base thickened into a bulb-scale, cut 

 across below to show its thickness. 



