174 



BOTANY 



PART I 



Piperaceae, Begoniaceae, species of Ficus, Tradescantia). The water- 

 storage tissue often has a more central position, and when largely 



developed gives the char- 

 acter of succulent plants. 



In rare cases the roots 



are transformed for water- 

 storage (e.g. Oxalis tetra- 



phylla). Leaf- succulents 



are more common (e.g. 



Sedum, Sempervivum, 



Agave, Aloe, Mesembryan- 



themum), while examples 



of stem -succulents are 



afforded by theCactaceae, 



species of Euphorbia, 



Stapelia, and other As- 



clepiadaceae (Figs. 197, 



200) and Kleinia among 



the Compositae. The 



columnar or spherical 

 Cactaceae are especially characteristic of arid regions in the new 

 world, while Euphorbias of similar habit take their place in the 

 eastern hemisphere. Similarity in the mode of life has thus 



FIG. 198. Part of stem and com- 

 pound leaf of Eobinia Pseud- 

 acacia, n, Stipules modified 

 into thorns ; g, pulvinus. 

 ( nat. size. After SCHENCK.) 



FIG. 199. Stem-thornof 

 Gleditschia triacanthos. 

 ( nat. size. After 

 SCHENCK.) 



FIG. 200. Plants with succulent steins, a, Stapelia grandijk>ra; ft, Cereus Pringlei ; 

 c, Euphorbia erosa. (| nat. size.) 



brought about a corresponding form in widely distinct plants (cf. Fig. 

 200, a-c). This phenomenon of CONVERGENCE OF CHARACTERS is not 

 infrequent. In extreme cases the form of the stem or the leaf of 

 succulent plants may approach that of a sphere ; this, for a given 



