k 



I-KSSON 0.] CONSOLIDATKI) 1 OUMS OK V KC KTATION, 47 



can hardly fail to obtain a prood idrji of what is niiaiit hy i)ii>rpli(>Ii>f/^ 

 in Botany ; and they will he al)lt! to apply its simple pi-inci|)le.s I'or 

 themselves to all forms of vegetation. Tiiey will find it very inter- 

 esting to identify all these varions subterranean forms with tiie com- 

 mon plan of vegetation above ground. There is the same strueture, 

 and the same mode of growth in reality, however diflerent in ap- 

 pearance, and however changed the form, to suit particular conditions, 

 or to accomplish particular ends. It is plain to sec, already, that 

 the plant is constructed accordhtg to a jylan, — a very simple one, — 

 which is exhibited by all vegetal)les, by the extraordinary no less 

 than by the ordinary kinds; and that the same organ may appear 

 under a great many different shapes, and fulfil very different offices. 



111. These extraordinary shapes are not confined to subterra- 

 nean vegetation. Tlusy arc all repeated in various sort^ of Jles/itf 

 plants; in the Ilouseleek, Aloe, Agave (Fig. 82), and in the man,, 

 and strange shapes which the Cactus family exhibit (Fig. 7G|. 

 shapes whicli imitate rootstocks, tubers, conns, &^q, above ground. 

 All these we may regard as 



115. Consolidatfll Forms of VrilClatinn. While ordinary jdants K 

 constructeil on the plan of great sjjread of surface (131), these 

 are formed on the j)lan of the least possible amount of surface iw, 

 proportion to their bulk. The Cereus genus of Cactuses, for ex- 

 ample, consisting of solid columnar trunks (Fig. 70, b), may be 

 likened to rootstocks. A green rind serves the purpose of foliag.,, 

 but the surface is at nothing compared with an ordinary leafy plant 

 of the same bulk. Compare, for instance, the largest Cactus known, 

 the Giant Cereus of the Gila River (Fig. 7G, in the background), 

 which rises to the height of fifty or sixty feet, with a common leafy 

 tree of the same height, such as that in Fig. 54, and estimate how 

 vastly greater, even without the foliage, the surface of the larter 

 is than that of the former. Compare, in the same view, an Op^./itiw' 

 or Prickly-Pear Cactus, its stem and branches formed of a si>v-es- 

 sion of thick and flattened joints (Fig. 70, a), which may be likened 

 to tubers, or an Epiphylhnn (d), with shorter and flatter joints, -ftith 

 an ordinary leafy shrub or herb of e(iual si/e. And finally, in 

 Melon-Cactuses or Kchinocactus (r), with their globular or bull)-like 

 shapes, we have jdants in tin; compactest sli:ipe ; (heir spherical fig- 

 ure Ix'ing such as to expose the lca>t possible amount of its bulk 

 to the air. 



1 10. These coHSolldiilcd jiJiiiils arc evidently adapted and d.->ignei^ 



