ASSIMILATING ROOTS : XEROPHYTISM 199 



§ 32. The Significance of Xerophytism 



In the account of the ways in which transpiration is 

 restricted, we have met with plants showing xerophytic 

 characters growing under a great variety of conditions, 

 ranging from stations in which the water supply is ample or 

 excessive and the transpiration on the whole low, as on the 

 moors of Northern Europe, to an environment in which 

 the most extreme aridity of soil is combined with untempered 



Fig. 33. — Podostemon. Nat. size. (After Warming.) 



insolation, as in the typical desert. The term xerophyte is 

 thus applied to the most varied types of plant growing under 

 the most diverse conditions. A definition of the term is by 

 no means easy to arrive at. As Delf (191 5), in a discussion 

 of the subject, in which a review of the work of previous 

 authors will be found, points out, xerophytism is sometimes 

 defined as a character of the plant and sometimes as a 

 character of the habitat ; the xerophyte is described as a 

 plant with certain structural features, or as a plant growing 

 in certain situations. Schimper combines the two ideas 



