CLASSES OF CRYPTOGAMS. 5 



spore-bearing, while the flowering are seed- 

 bearing. The flowerless plants are far the 

 more numerous, and the greater part of 

 them are as yet very imperfectly understood. 

 On account of our imperfect knowledge of 

 them, together with numerous difficulties in 

 the way of studying the lower species, there 

 is no generally accepted method of classify- 

 ing them. For our purpose it is sufficient 

 to say that flowerless plants are divided into 

 Fungi, Algae, Lichens, Mosses, and Ferns. 

 There are two important facts, which we 

 may profitably consider, relating to the 

 methods by which these plants gain sus- 

 tenance. There are two classes of plant 

 foods : one is composed of substances which 

 are found in the earth and the air, such as 

 water, carbonic acid gas, lime, potash, and 

 ammonia, commonly designated inorganic 

 substances ; the other is composed of mate- 

 rials which are made out of these inorganic 

 substances by the plant itself, such as woody 

 fibre, starch, and other vegetable or organic 

 products. Most of the plants which we ob- 

 serve possess the power of making over in- 

 organic or earthy materials into organized 

 or vegetable materials ; or, in technical lan- 

 guage, they assimilate. All such plants con- 



