318 FOUNDATIONS OF BOTANY 



from Part I of this book about the forms, structure, and 

 habits of ordinary plants, together with what the student's 

 own observation, aside from the study of botany, has taught 

 him, should suffice to give him a fair idea of mesophytic 

 plant life. 



The typical mesophyte of the northern United States is 

 an annual, since most of our larger perennials pass the 

 winter in a xerophytic condition, to avoid destruction by 

 drying up during the long period when 

 the roots can absorb little or no water 



FIG. 225. Cross-Section of Leaves of a Grass, 1 unrolled for Exposure to 

 Sunlight and rolled up to prevent Evaporation. 



r, ridges of the upper epidermis, with many stomata on their surfaces ; 

 e, thick lower epidermis, without stomata. 



from the frozen soil. Our evergreen coniferous trees, 

 such as pines, spruces, cedars, and so on, have leaves of 

 decidedly xerophytic structure. So also do such ever- 

 green shrubs as the rhododendrons, wintergreen, arbutus, 

 holly, and bearberry. Our deciduous trees and shrubs and 

 most perennial herbs are tropophytes (Sect. 390). 



390. Tropophytes, or Seasonal Plants. Examples of 

 these are most deciduous trees and the majority of the 

 perennials of temperate regions, for instance oaks, elms, 

 birches among trees, and tulips, crown imperials, lilies, 

 hyacinths, spring-beauties, peonies, dahlias, and potatoes 

 among herbs. Such plants have a pretty large surface for 



1 Stipa capillata. 



