26 The Great World's Farm 



indeed, "and consume more mineral matter in proportion 

 to their size than any other plants. 



But if it is locked up, and not available until the rock 

 is crumbled down and softened enough for the roots to 

 penetrate into it, how can they get at it? 



In one respect lichens are like seaweeds, for they have 

 no roots through which to take up food. But they are 

 unlike them in another, for they do feed upon the rocks; 

 and even these first-comers, the humblest members of the 

 family, mere stains in appearance, contrive to make a 

 living wherever they can gain a footing. Not, of course, 

 that they take up particles of stone, but being all of them 

 strongly acid, they are able to dissolve it first and then 

 absorb what they need; and though they are at first so 

 minute as to be almost microscopic, no rock can resist 

 them. 



The ** stains" spread and grow and decay, and by 

 degrees there is formed from their remains a thin film of 

 soil, in which lichens of a much larger growth are able to 

 flourish. They are all more or less harsh to the touch; 

 and the ashy, steely grays, and rusty browns, and the 

 brilliant yellow and orange of their coloring remind one 

 more of minerals than of vegetables, which is not surpris- 

 ing, considering that often a fifth part of their substance, 

 and sometimes much more, consists of solid matter eaten 

 from the rocks. 



When the lichens have had possession for a time, and 

 have prepared the way, they are followed by mosses, 

 which absorb much moisture from the air, and help to 

 decay the rock by keeping the surface damp; for, as we 

 have already seen, where water is, there frost and gases 

 can get to work. The mosses grow and die in their turn. 



