ABSORPTION OF ASH-CONSTITUENTS 



79 



Calcium is likewise necessary, especially for normal leaf development. Some 

 plants without chlorophyll (movilds) can exist without calcium/ and non-green 

 phanerogams contain much less calcium than do green plants.* 



Magnesium is also necessary; it accompanies proteins and is contained in 

 chlorophyll. 



Finally, plants need iron, the lack of which prevents chlorophyll formation; 

 they become pale and chlorotic,' even in the light, when grown without this 

 element. 



§3. Importance of the Non-essential'Ash-constituents. — Plant ash contains 

 appreciable quantities of other elements than the absolutely essential ones, and 



Fid. 51. — Portion of a cross-section through a rye stalk. ^, lodged; B, normal. {After Koch.) 



these are not to be considered as entirely without physiological effects. Each 

 ash-constituent must be considered as exerting some slight effect in the plant, 

 either injiirious or beneficial. If plants develop apparently normally in a nutri- 

 ent solution without a given element, it does not necessarily follow that this 

 element, if present, might not exert some beneficial influence. 



Silicon, for example, is abundant in many plants. Nevertheless, experi- 

 ments with various plants in artificial media have shown that even the grasses 



> Loew, Oscar, Limiog of soils from a physiological standpoint. U. S. Dept, Agric. Bull. 1. 27 p. 

 Washington, 1901, 



>Asa, K., On the lime content of phanerogamic parasites. Bull. Coll. Agric. Imp. Univ. Tokyo 

 4: 387-389- 1900-1902. 



> Molisch, 1892. [See note 6, p. 50.] 



