376 THE UNIVERSE. 



ter green and fresh for a long time. Therefore the one ab- 

 sorbed for the other. 



We must not omit stating that there are even certain 

 plants in which this function is entirely displaced ; the task 

 is confided to the stem only. This is the case with the cac- 

 tuses, strange existences, which consist solely of a 

 monstrously swollen stem covered with spines. Growing 

 only among rocks and sands parched by the sun, where all 

 other plants around them wither into dust, these corpulent 

 plants exhibit a freshness which is inexplicable. By some 

 secret, unknown to the myriads of different kinds, the desic- 

 cated corpses of which surround them, they contrive to im- 

 bibe from the atmosphere the abundance of water which 

 swells out their tissues. Among these " heralds of ruined 

 soils," as Ch. Miiller calls them, the roots, represented only 

 by a few dried fibres, draw absolutely nothing from the cal- 

 cined rock which supports them. It is therefore the stem 

 which nourishes itself ; the leaves are so rudimentary, so 

 little apparent, that it may be looked upon as entirely de- 

 prived of them. 



In our hot-houses the same thing may be seen every day. 

 Cactuses, which are never watered, thrive there splendidly 

 by means of the moist and warm atmosphere with which 

 they are surrounded. 



