IO 



THE FACTORS [Part I 



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

 hereditary. 



It has been already pointed out that many plants growing in dry places 



Fig. 1 1 . Xerophilous structure. Dry substratum of tree-bark and rocks, i . Octomeria sp. 

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



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

 in the vegetation of dry stations— if they be not universally present. They 

 are sometimes thin-walled living cells, sometimes dead cells like tracheids, 



