Chapter XLI. 



Hydrophytic Plants. 



The different adaptational groups of plants may be best 

 classified under three main divisions, according to the relation 

 between the structure of the plant and the moisture of sur- 

 rounding conditions. For one series of plants the moisture 

 of the surroundings may be considerable, for another it is ordi- 

 narily slight, while for the third a middle condition is main- 

 tained. Thus, there are three principal adaptational groups, 

 known respectively as hydrophytes, of which aquatic species 

 are typical; xerophytes, of which desert inhabitants are char- 

 acteristic forms ; and mesophytes, in which group may be classi- 

 fied the common herbs of meadow and forest, growing under 

 medium conditions of moisture. It should be noted in pass- 

 ing that while the essential structural adaptation of desert 

 plants is toward the slow evaporation of moisture, there are 

 also other conditions, besides those of desert life, that make 

 rapid evaporation undesirable. Hence plants growing in 

 peat-bogs, such as tamaracks and spruces, or plants grow- 

 ing in saline localities are said to have the xerophytic type of 

 structure and, like true desert plants, are slow to transpire 

 moisture. A number of different subdivisions of the three 

 main classes may be described, and one should regard the marsh 

 and swamp varieties, and those living in saline soil, as furnishing 

 the transition to the true middle group, that of the mesophytes, 

 which will here be discussed after a brief account of the other 

 two. 



Out of fourteen classes of hydrophytic plants described by 

 Eugene Warming, in his classic work upon adaptational groups 

 of plants, eight are represented in Minnesota. Those unrep- 

 resented are either arctic or alpine, such as the snow plants, 

 or marine, such as the seaweeds, and the mangrove swamps 

 of oceanic coast lines. 



