CACTI AND EUPHORBIAS 



water through the leaves. When the skin or epidermis of a 

 plant is being formed, the walls of its cells are laid down, 

 layer by layer, one inside the other, by the secretion of the 

 living matter inside. In a dry desert the loss of water by 

 evaporation will be so rapid that these layers of cell-wall are 

 much thicker than in ordinary plants. The very fact that 

 they are thicker and less penetrable tends to prevent any 

 further loss of water. ^ 



So that plants in a dry climate have the power of altering 

 themselves to resist its dangers. 



Another author found that, in Scandinavia, plants of the 

 same species can acclimatize themselves if necessary. Sheep's 

 Sorrel which had grown on dry, droughty gravel banks only 

 lost 10 per cent of its water in the first two days, when it 

 was artificially dried. Other Sheep's Sorrels, which had been 

 luxuriating in meadows where they had no lack of moisture, 

 lost no less than one third (33 per cent) of their water when 

 dried in the same way. 



That is interesting, because very likely our readers might 

 in crossing a desert be perishing of thirst when a Bedouin 

 Arab would be perfectly happy. The plants have learnt to 

 do without water just in the same way as the Arab has done. 



Of the many interesting desert plants, the Succulents, 

 Cacti, Euphorbias, and others of the same extraordinary, 

 fleshy, dropsical appearance, come first. 



When a Cereus plant (one of the American Giant Cacti) 

 was dried, it did not lose the whole of its water for 576 days. 

 That is probably the longest time "between drinks" on 

 record. A Houseleek (Sempervivum), which has to grow on 

 dry rocks where it has no water for days together, remained 

 quite fresh for 165 days. 



^ Schimper, I.e., p. 653. 

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