THEIR VALUE. 347 



tive surface, there would be a deterioration of the 

 portion left. The soil which immediately pro- 

 duces 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 valleys 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 na- 

 tive 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 &oil is 

 not much lessened in its quantity, while it is soft- 

 ened 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 tem- 

 perature that kills plants, it is the greatness 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 



