464 



CACTUSES IN- DOORS AND OUT. 



cactus-like euphorbias are very abundant ; and the leaf- 

 bearing kinds, E .bahamifera and E. Regis- Julm, are also 

 prominent among the other endemic forms. 



" Many of the euphorbias of the Oceanic Islands re- 

 semble those of the Soudan, thus forming a connecting 

 link between the vegetation of these islands and Africa." 



All this stretch of vision leads us to the still broader 

 ambition to know what are the general peculiarities of 



ics, and separate the region of the periodic rains from 

 the region of irregular rains by two broad belts of coun- 

 try, in which the xerophilous plants predominate more 

 decidedly tban they do in any other part of the world, 

 and that they run out from these belts into the interior 

 of the continents, both towards the equator and the 

 poles, avoiding the insular climates. 



"The concomitants in plant-form of the xerophilous 



Fig. O. Leuchtenbergia principis. 



xerophilous or desert plants and regions. And here we 

 can do no better than to quote Baker in his inimitable 

 sketch of Botanical Geography, omitting some of the ex- 

 amples : 



"Broadly stated, the grand influence which the dis- 

 tribution of moisture over the earth's surface exercises 

 upon the distribution of plants is that the earth is girdled 

 round, in and near the borders of the two rainless zones, 

 which run like a belt round the earth near the two trop- 



type of constitution are as follows : In dicotyledons 

 (or netted-leaved plants) — ist, leaves becoming thick 

 and fleshy, with pulpy inner and leathery outer layers, 

 in which the air passages and stomata are few, and the 

 cells either small or their walls thickened by secondary 

 deposits of cellulose, as shown in mesembryanthemum, 

 sedum, cotyledon and sempervivum ; 2nd, the stem 

 condensed into a single central, unbranched, barrel- 

 shaped or top-shaped mass, which is either leafless, and 



