July 17, 1916 Influence of Calcium and Magnesium on Plant Growth 613 



TABLE XXI. Tolerance of crops for calcium and magnesium 



The yields in the pots in Table XXI were practically the same on the 

 different treatments. This shows the alfalfa to contain more calcium 

 and magnesium than the wheat. Some of the other treatments show 

 higher percentages of calcium and magnesium, but the yields are not com- 

 parable. It might be interesting to note that soybean hay at maturity 

 contained per ton as much as 73 pounds of calcium and 25.2 pounds of 

 magnesium when grown in a mixture of equal parts of sand and calcareous 

 soil,, but when grown in a mixture containing 40 per cent of magnesite 



there were 22.9 pounds of calcium and 43.3 pounds of magnesium per ton. 

 f 



DISCUSSION 



The experiments reported here extend over a period of three years 

 (1912 to 1915) and include approximately 300 pot cultures and upwards 

 of 300 duplicate determinations of calcium and magnesium. 



Difficulty was experienced in finding a medium that was free from 

 calcium and magnesium, and which would still approach soil conditions. 

 Attempts were made to grow plants in aluminum turnings but without 

 success, probably due to the formation of some aluminum salts when the 

 plant foods were added. It is well known that aluminum salts disturb 

 the physiological functioning of plant organs. 



Wheat and cowpeas grown in granular paraffin without the addition 

 of calcium and magnesium showed in the total plant only an amount 

 equal to that furnished by the seed. 



