176 Plant Physiology 



has suggested a cause of this use and disuse. When the 

 benefits from it at any time became known, this probably 

 led to excessive use, causing injury, whereby the practice 

 again fell into disfavor. In the United States a careful 

 study of the liming practice and of its effects has been 

 made in comparatively recent years. 



Calcium has functions to perform which are strictly 

 physiological; that is, directly important in the metabolism 

 of the plant ; it has other effects distinctly ecological, 

 affecting the plant through its action upon the physical 

 and chemical environment. . It is not always possible to 

 distinguish the one form of effect from the other. From 

 an agricultural standpoint Wheeler has given in the "Cyclo- 

 pedia of American Agriculture " a concise enumeration of 

 the effects. In this connection the physiological side re- 

 quires more particular consideration. 



In vegetative organs. There is generally a considerable 

 accumulation of lime in leaves and other vegetative organs, 

 and on this account it has been assumed to play an impor- 

 tant role in some of the functions associated with the 

 chlorophyll. Up to a certain point calcium hunger does 

 not affect starch formation, and the evidence points rather 

 to an inhibition of .starch and other carbohydrate diges- 

 tion and transport. In fact, many fundamental experi- 

 ments have established a definite relation whether 

 direct or indirect it is impossible to say between calcium 

 content and starch digestion. The addition of soluble 

 carbohydrates is generally beneficial where plants lack 

 calcium. In this connection it is of interest to note that 

 calcium is apparently not required by fungi and some 

 of the lower algae, yet it is required by higher plants 

 forming no starch. 



