Mosses. 341 



often acts in the most beautiful hygrometrical manner. If you 

 take the theca of this Tortula, for example, when dry, and put 

 it in a damp place, or in water, its teeth will uncoil, and disen- 

 tangle themselves with a graceful and steady motion, which is 

 beautiful to look upon. 



It is in the inside of the theca that the spores are confined. 

 They lie there in a thin bag, which is open at the upper end, 

 and which surrounds a central column, called the columella. 

 They are exceeding^ minute, and not unlike the spores 

 of Ferns. The study of the distinctions of Mosses, requires 

 great care and attention, and much skill in the use of the micro- 

 scope. It has sometimes occupied the undivided attention of 

 botanists, and cannot be prosecuted without much leisure and 

 patience. 



When we quit Mosses and other plants of a similar nature, 

 we find ourselves among beings in which all traces of stem 

 and leaves have disappeared, and which consist of nothing 

 but thin horizontal expansions of vegetable matter, in which a 

 few harder, and differently formed kernels or shields are im- 

 bedded. In some of these the color is yellow, brown, or 

 green ; the texture of the expansion leafy ; and the margin cut 

 up into many lobes — these are most nearly related to leafy and 

 more perfect plants. In others, the expansion is merely a thin 

 crust, which readily crumbles in pieces, the species having 

 scarcely vital energy enough to keep the cells of which they 

 are composed in a state of cohesion. Such plants as these are 

 called Lichens. They are found chiefly in the temperate or 

 colder regions of the earth. Some of them crawl upon the 

 surface of the earth, spreading their dingy, cold, and damp 

 bodies over whole plains in the desolate regions of the north : 

 others spring up on the branches of trees, and hang down from 

 them like gray and netted beards, giving the unfortunate plants 

 of which they take possession a hoary, wintry aspect, even in 

 summer: -some overrun old walls, stones, and rocks, to which 

 they communicate those wild and agreeable tints, which ren- 

 der ancient ruins so pleasing to the eye ; and, finally, a fourth 

 description of Lichens establish themselves upon the bark of 

 living trees, occasionally burying themselves beneath the skin 



