LESSON 6.] CONSOLIDATED FORMS OF TEGETATION. 47 



can hardly fail to obtain a good idea of what is meant by morphology 

 in Botany ; and they wiU be able to apply its simple principles for 

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

 esting to identify all these various subterranean forms with the com- 

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

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

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

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

 the plant is constructed according to a flan, — a very simple one, — 

 which is exhibited by all vegetables, 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. 



114. These extraordinary shapes are not confined to subterra- 

 nean vegetation. They are all repeated in various sorts oi fleshy 

 plants ; in the Houseleek, Aloe, Agave (Fig. 82), and in the many 

 and strange shapes which the Cactus family exhibit (Fig. 76) ; 

 shapes which imitate rootstocks, tubers, corms, &c. above ground. 

 All these we may regard as 



115. Consolidated Forms of Vegetation. While ordinary plants are 

 constructed on the plan of great spread of surface (131), these 

 are formed on the plan of the least possible amount of surface in 

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

 ample, consisting of solid columnar trunks (Fig. 76, J), may be 

 likened to rootstocks. A green rind serves the purpose of foliage ; 

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

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

 the Giant Cereus of the Gila River (Fig. 76, 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 latter 

 is than that of the former. Compare, in the same view, an Opuntia 

 or Prickly-Pear Cactus, its stem and branches formed of a succes- 

 sion of thick and flattened joints (Fig. 76, a), which may be likened 

 to tubers, or an Epiphyllum (d), with shorter and flatter joints, with 

 an ordinary leafy shrub or herb of equal size. And finally, in 

 Melon-Cactuses or Echinocactus (c), with their globular or bulb-like 

 shapes, we have plants in the compactest shape ; their spherical fig- 

 ure being such as to expose the least possible amount of its bulk 

 to the air. 



116. These consolidated plants are evidently adapted and designed 



