lO 



THE FACTORS 



[Part I 



whilst in other plants, such as Eucalyptus, the position has become 



hereditary. 



It has been already pointed out that maj}x.plant Lgro\ving in dry places 



Fig. h. Xerophilous structure. Dry substratum of tree-bark androcks. i. Octomeria sp. 

 2. Cattleya bicolor. Desterro, Brazil. Natural size. 



develop water-storing cells. Such water-reservoirs are constantly met with 

 in the vegetation ot dry stations — if they be not universally present. The y 

 are sometimes thin-waljed— living- ^ells, somelioes dead cells like tracheids, 



