322 THEIR VALUE. 



all the mould of the heights into the valleys, and the 

 portion of land fit forbearing vegetables of any kind 

 would decrease every year. Nor would there be 

 merely a decrease of the productive surface, there 

 would be a deterioration of the portion left. The 

 soil which immediately produces the mosses, and 

 lichens, and other plants of the high and cold 

 grounds, is not adapted for the production of the soft 

 grasses and flowers of the valleys: and these val- 

 leys are not suited in climate for the upland plants, 

 though those plants and the soil in which they grow 

 both tend to cool the climate and bring it nearer to 

 their native one. Thus, if these plants were to 

 "give way" in the autumn, as is the case with 

 many of the plants lower down, the meadows would 

 annually be strewed with unwholesome earth, which 

 would in time destroy their fertility, and they would 

 become bogs and quagmires. But the matting of 

 mosses and lichens keeps the soil together, and 

 equally prevents it from being washed away by the 

 rains, and blown away by the winds ; so that when 

 the cold weather comes the soil is not much lessened 

 in its quantity, while it is softened and divided by 

 the frost, and thereby fitted for the action of the 

 roots of those plants, the stems of which die down 

 annually. In plants of that kind, more especially in 

 those that have fleshy or bulbous roots, which most 

 of the plants that die down in the winter in cold 

 places have, the crown of the root is usually the 

 vital part, so that if that sustains much injury the 

 plant is killed. Now the winter crop of mosses is 

 of great service to plants of that kind. It is not the 

 absolute temperature that kills plants, it is the great- 

 ness and especially the rapidity of the changes ; and 

 if the operation could be performed gradually enough, 

 it is possible that any plant (even those which are kept 

 in the artificial heat of stoves in this country) could 

 not only bear the frost, but actually to be frozen 

 without much injury. The progress of ordinary 



