1 66 AGRICULTURAL CHEMISTRY 



slum in its chemical deportment, is not absolutely neces- 

 sary for agricultural plants and does not occur in the ash 

 in such large amounts as potassium. Nearly all agricul- 

 tural plants are brought to maturity without its aid 

 except for the small amount in the seed. The amount, 

 if any, which plants require is very small, not sufficient 

 to take into consideration. It is supposed to be present 

 as an accidental ingredient, because sodium chlorid is 

 universally present in the soil, in water, and occasionally 

 traces of it are in the air ; hence plants could not very 

 well exclude it. Some alkali plants require and store up 

 large amounts of sodium compounds. Unlike potassium, 

 sodium is not so evenly distributed through the plant. 

 It has no special movement, but is found mostly in the 

 lower parts of the plant. Seeds contain but little of it, 

 more being present in the straw and stems. 



215. Calcium. This element is always present in the 

 ash of plants. None of the higher plants can reach 

 maturity without a normal supply. Some, like clover, 

 beans, peas, and lucern, require so much for their develop- 

 ment that they are called ' ' lime plants. ' ' Accumula- 

 tions of lime are found in many leafy plants, particularly 

 clover, where crystals of calcium oxalate may be 

 observed. In leaves, it appears to have the special func- 

 tion of aiding in the construction of the cell walls. 

 No new plant cells can be produced without the aid of 

 calcium. 



From the culture experiments of various investigators, 

 the element calcium appears to take a prominent part in 

 the production of new tissues. Whenever it is withheld, 



