96 THE HEATH. 



ment through their leaves and stems, the mosses 

 and lichens, and especially the latter, have no 

 need of roots, properly so called ; all that they 

 require, is, to be attached to the rock so firmly 

 as to be able to resist the action of the wind, 

 which in exposed places like those in which they 

 grow, is at times very violent. And firmly at- 

 tached they are indeed ; for although you may 

 readily remove a part of a plant from the rock, 

 you will find it a far easier task to detach a por- 

 tion of the rock from the mass, than to separate 

 from it the extremity of the stem. Having then 

 no means for deriving nourishment from the sub- 

 stance on which they grow, and growing on a sub- 

 stance which can afford them none, situated in 

 localities which are exposed to the direct rays of 

 the sun, and the immediate action of the wind, 

 if like most other plants, they could not live with- 

 out the constant presence of moisture, the first 

 week of hot summer weather, or of a dry east 

 wind, would terminate their existence, and the 

 whole tribe not having time to mature their seeds, 

 would perish. Thus we see, that their constitu- 

 tion is such as eminently suits them for growing 

 in places where no other vegetable would live. 



And now as to their utility. Those which 

 appear first in order of time, are the hard thin 

 lichens ; which I first described. Their rough 

 surface arrests, and retains the seeds of the larger 

 kinds lodged on them by the wind. These ger- 

 minate ; and while, during their term of existence, 

 they in like manner arrest the particles of dust 

 which may be brought by the wind, they eventually 

 decay, and afford in their mouldering substance a 

 suitable resting-place for the seeds of grasses, 



