64 MORPHOLOGY OF STEMS. 



the Garlic (Fig. 115) ; 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 individuals. So the corm 

 of the Crocus (Fig. Ill, 112) produces one or more new ones, 

 which feed upon and exhaust it, and take its place ; and the 

 next season the shrivelled remains of the old corm may be found 

 underneath the new. The corm of Colchicum (Fig. 117) pro- 

 duces 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. The figure represents at one view, a, the dead and 

 shrivelled corm of the year preceding ; 6, that of the present 

 season (in a vertical section) ; and, c, the nascent bud for the 

 growth of the ensuing year. 



125. Condensed Stems, homologous with corms, tubers, &c., 

 and similar in mode of growth, but above ground, and multiply- 

 ing in the same ways, are not uncommon. The Cactus famiby is 

 mainly composed of such forms, of flat- or round-jointed Prickly 

 Pears (Opuntia) , fluted or angled columns (Cereus) , and glob- 

 ular Melon-Cactus, Mamillaria, and Echinocactus. The latter 

 types, which completely imitate corms, are the most consolidated 

 forms of vegetation. While ordinary plants are constructed on 

 the plan of great expansion of surface, these present the least 

 possible amount of surface in proportion to their bulk, their 

 permanent spherical figure being that which exposes the smallest 

 portion of their substance to the air. Such plants are evidently 

 adapted to very dry regions ; and in such only are they naturally 

 found. Similarly, bulbous and corm-bearing plants, and the 

 like, are a form of vegetation which in the growing season may 

 in the foliage expand a large surface to the air and light, while 

 during the period of rest the living vegetable is reduced to a 

 globular or other form of the least surface ; and this is protected 

 by its outer coats of dead and dry scales, as well as by its subter- 

 ranean situation ; thus exhibiting another and very similar 

 adaptation to a season of drought. And such plants mainly 

 belong to countries (such as Southern Africa, and the interior 

 of Oregon and California) which have a long hot season, during 

 which little or no rain falls, when, their stalks and foliage above 

 and their roots beneath being early cut off by drought, the plants 

 rest securely in the corm-like forms to which they are reduced, 

 and retain their moisture with great tenacity until the rain}' season 

 returns. Then they shoot forth leaves and flowers with wonderful 

 rapidity, and what was perhaps a desert of arid sand becomes 

 green with foliage and gay with blossoms, almost in a day. 



