THE VEGETABLE KINGDOM. 375 



them grow with as much rapidity as if their roots were 

 moistened. Some spongy plants, gorged with aqueous fluid, 

 seem to draw their nourishment exclusively from the atmos- 

 phere. It is thus that in the burning days of summer I 

 have found carpets of ice-plants on the most arid rocks in 

 Greece. Although it had not rained for a month, these 

 plants displayed a remarkable freshness, and their leaves 

 were none the less covered with a coating of icicles ! l 



The absorption effected by the leaves was known to the 

 ancients. Theophrastus makes mention of it, but we must 

 come to the epoch of Mariotte to reach the demonstration 



177. Absorption by the Leaves. Mariotte's experiment. 



of this phenomenon, which the Greek botanist had only 

 pointed out. The French philosopher attained this result 

 by means of a very simple experiment. He took a bifur- 

 cated branch, and placed one part of it in a vessel filled 

 with water, while the other remained exposed to the air. 

 The water absorbed by the former sufficed to keep the lat- 



1 The glacial Mesembryanthemum crystallinum is a small herbaceous plant, well 

 known in science on account of its strange appearance. It has literally the look 

 of a plant covered with drops of frozen water. This appearance is due to exces- 

 sive development of all the superficial cells of the plant, which are like so many 

 small bags filled with limpid water. 



