ADAPTATION TO WATER 



169 



total water content is excessive. It has been shown, however that 

 the presence of acids increases the absorption of water. Conse- 

 quently, it seems absolutely impossible for small quantities of 

 humic acids to produce xerophytes in ponds and bogs. Their 

 influence would tend to make water plants even more hydrophytic. 

 Moreover, in many ponds and swamps where leafless sedges and 



Fig. 57. A bog plant, Sagittaria latifolia. The large plant represents the 

 normal form, while the small one in the pot is a xerophytic form arti- 

 ficially produced to prove that the normal form is not a xcrophyte. 



rushes grow, not a trace of acids can be discovered. Furthermore, 

 plants which are typical hydrophytes throughout, such as Caltha, 

 Ludwigia, Ranunculus, and Sagittaria, are regularly found grow- 

 ing alongside of these apparent xerophytes. It is imjiossible 

 for the same habitat to produce both hydrophytes and xerojihytes. 

 Many of the so-called bog xerophytes possess structures, such as 

 air passages, diaphragms, etc., which are peculiar to hydro])hytes. 

 This is especially true of the form and structure of the root system. 



