110 



THK STEM. 



of the stem, grow and branch, or multiply, by the development of 

 terminal and axillary buds. This is perfectly evident in the rhizoma 

 and tuber, and is equally the case in the corm and bulb. The stem 

 of the bulb is usually reduced to a mere plate (Fig. 178, a), which 

 produces roots from its lower sui-face, and leaves or scales from the 

 upper surface. Besides the terminal bud (c), wliich usually fomis 

 the flower-stem, lateral buds (S, b) are produced in the axils of the 

 leaves or scales. One or more of these may develop as flowering 

 stems the next season, and thus the same bulb survive and blossom 

 from year to year ; or these axillary buds may themselves become 

 bulbs, feeding on the parent bulb, which in this way is often con- 

 sumed by its own offspring, as in tte Garlic (Fig. 179) ; or, finally 

 separating from the living parent, just as the bulblets of the Tiger 

 Lily fall from the stem, they may form so many independent indi- 

 viduals. So the corm of the Crocus (Fig. 

 182, 182") produces one or more new ones, 

 which feed upon and exhaust it, and take its 

 place ; and the shrivelled remains of the old 

 corm may be found underneath the new, the 

 next season. The corm of Colchicum (Fig. 

 181) produces a new bud on one side at the 

 base, and is consumed by it in the course of 

 the season ; the new one, after flowering by 

 its terminal bud, is in turn consumed by its 

 own offspring; and so on. In Fig. 181, we 

 have at one view, a, the dead and shrivelled 

 corm of the year preceding ; b, that of the 

 present sea-on (a vertical section) ; and c, 

 the nascent bud for the growth of the ensuing 

 season. Many of the forms which the stem assumes when above 

 ground differ as much from the ordinary appearance as do any of 

 these subterranean kinds, and, in fact, imitate their peculiarities ; as, 

 for example, the globular Melon-Cactus and Mamillaria, the colum- 

 nar Cereus, and the jointed Opuntia or Prickly Pear. These are 

 remarkably 



194. Consolidated Forms of Vegetation. While ordinary plants are 



constructed on the plan of great expansion of surface, these are 



FIG. 182. Corm of Crocus, the few thin enveloping scales removed, showing the shrivelled 

 vestige of the last year's conn at the hMe, and buds developing into new ones on various 

 parts of its surfaeo. 182° Vertical section of a similar corm, with a terminal and one lateral 

 bud. 



