280 



GENERAL PHFSIOLOGY 



appear like small crystal droplets (Fig. 127). These desert-plants 

 have a remarkable power of retaining water, either by storing up in 

 their cell-sap soluble substances that possess great attraction for 

 water, or by being covered over their whole surface with a fine layer 

 of wax, so that with the stomata closed scarcely a trace of water can 

 pass by evaporation out of the plant-body. Moreover, they possess 

 usually much-branched roots extending very far and superficially in 

 the soil, and these greedily suck up every trace of water that 

 moistens the earth. The desert-animals also, such as the snails, 



Pig. 127. 



—Menemh'njanthemv.m cryatallinura, a desert-plant from Southern Africa. The whole stem 

 and the under side of the leaves are beset with clear crystal-like water-cells. 



which are confined to their dry home because of their slight powers 

 of locomotion, protect themselves by limiting their excretion of 

 water to a minimum. The snails close the opening of their shells 

 with a thick, double cover, so that scarcely a trace of water can be 

 lost from the body by evaporation. Hence, in all these cases the 

 dryness of the environment does not extend to the living sub- 

 stance of the organisms. On the contrary, here, as everywhere, 

 the living substance is liquid, and in fact all desert-organisms 

 have an actual, not a latent, life, although their life is depressed to a 

 minimum. The}' show directly how the intensity of life increases 



