312 



FOUNDATIONS OF BOTANY 



is in dividing mesophytes from tlie other two classes, into 

 which they shade by indefinite gradations. In order to 

 know whether the plants of a region have plenty of water 

 or not, we must know not only how many inches of yearly 

 rainfall there are, but also what the soil is like, what is 

 the temperature, of the soil and air, whether or not there 

 are dry winds, and whether there are 

 fogs or heavy dews. A lichen on a 

 bare rock may be living almost under 



Fis. 218. ^Aquatic Plants : Pond-Lilies with Floating Leaves and 

 Sedges -vrith ASrial Leaves. 



desert conditions, while a pitcher-plant in a bog near by 

 has its roots in standing water (or in ice) nearly all the 

 year round. 



384. Hydrophytes. — Some of these are herbaceous 

 aquatic plants, like the duckweed, the pickerel-weed, 

 the pond-lily, and the water-crowfoot ; others, such as the 

 "calla" (Bichardia), the buckbean, the cat-tail, and the 

 sweet flag, many ferns, mosses, and liverworts, prefer 



