THE ABSORPTION OF MINERAL ELEMENTS 



93 



In their relationship to the calcium content of the soil plants 

 may be divided in two great groups; those which like lime, or 

 calciophiles, and those that avoid lime, calciophobes. These two 

 groups are linked by a series of intermediate plants. They may 

 be sharply separated only by considering their extreme repre- 

 sentatives. These differences, however, are of a purely physio- 

 logical character. They cannot be distinguished by any anatom- 

 ical or morphological peculiarities. 



Fig. 39. — Salicornia plants growing without sodium chloride, on the left; and 

 with the addition of sodium chloride, on the right {after Keller). 



Not many of the higher plants are definitely calciophobes. 

 Good examples of such plants are the chestnut (Castanea vesca), 

 sphagnum moss, and several other plants of sphagnum bogs. 



As calcium represents one of the indispensable elements for 

 the development of higher plants, it seems at first sight incompre- 

 hensible how there can be plants which do not grow on calcareous 

 soils. Yet the ash of such lime-avoiding plants contains normal 

 amounts of CaO. This becomes understandable, however, if it is 

 remembered that an increased or decreased lime content results in 

 chemical and physical changes of the soil. Soils that contain 

 much lime have a neutral or slightly alkaline reaction advan- 



