THE STORY OF THE LICHENS "S 



light matter. Of course, there is no doubt 

 that those kinds of Hchens which spread over 

 the surface of the ground, or grow over tree 

 trunks, will be able to absorb a good deal of 

 water directly, but even in such situations they 

 must rely to a considerable extent upon the 

 moisture which they can draw from the atmo- 

 sphere. In the case of those lichens, such as 

 the Old Man's Beard, which hang down from 

 the branches of trees and are only attached in 

 one place, the difficulty of securing a suffi- 

 ciency of water is even more perplexing. By 

 their very formation lichens are well adapted 

 for absorbing watery vapour from the air. 

 During the summer, when they are dry, lichens 

 suspended in a moist atmosphere, such as is 

 induced by the steam issuing from a kettle, will 

 quickly become damp and flabby — a marked 

 contrast to the crisp and brittle condition in 

 which they were a few moments previously. It 

 goes without saying that plants which take up 

 moisture so readily from the air will no less 

 quickly lose it by evaporation when the atmo- 

 sphere is warm and dr3^ It has been seen, 

 however, that lichens seem to be best able to 

 withstand extremes of heat, cold, and drought. 



