CELLUIiAEES, OR CELLULAR PLANTS. 67 



82. Few common objects are more interesting than mosses, 

 •whicb. require neither skill nor the assistance of instruments 

 for the detection of their beauties. The term moss is applied 

 not only to the true mosses, but also to many lichens. The 

 true mosses may, however, be always distinguished by their 

 green color, whilst the lichens are generally grayish in their 

 aspect, or of some other hue than green. 



83. In the algse and lichens there are no fixed forms as- 

 sumed by these plants ; they are also, generally, without any 

 local habitat. Some of the lichens vegetate indifierently 

 anywhere, on rocks, or the bark of trees, or on the ground, 

 and vegetate in all climates, and at all seasons of the year. 

 These plants certainly exhibit a low degree of life as well as 

 simplicity of organization. They are amongst the slowest 

 in growth of all plants, and the least subject to alteration 

 from decay. Whilst alive, they scarcely exhibit any change 

 through a long series of years; and, when dead, their forms 

 and colors are scarcely altered by being dried. 



84. But we are ascending the scale ; and now commences 

 the unfolding of a more elaborate organization, in which the 

 conditions of development are necessarily more restricted, 

 and a higher degree of life is manifested. The plants now 

 about to be described grow only in certain soils, at certain 

 seasons of the year, and are peculiar to certain climates, 

 whilst they retain the same specific form from age to age. 



85. Mosses generally affect a cool, moist, shady situation, 

 and appear to be for the most part developed under the in- 

 fluence of humidity, accompanied with a low degree of tem- 

 perature. Hence they prefer the shade of woods and rocks 



