July 17, 1916 Influence of Calcium and Magnesium on Plant Growth 615 



and 42.3 pounds of magnesium per ton; whereas the checks contained 

 5.8 pounds of calcium and 5.6 pounds of magnesium. 



Whenever excessive amounts of magnesium were applied, there was 

 a characteristic appearance of yellow leaves. The uppermost leaves be- 

 came yellow and gradually died, while the lower leaves remained green. 

 This condition is characteristic of magnesium sickness and just the re- 

 verse of the effects produced by translocation processes. 



The general tendency is for the percentages of calcium and magne- 

 sium in the plants to increase with the increase in size of application. 

 Likewise a high magnesium content in the plant tends to accompany 

 plant sickness, as sickly and healthy leaves from x the same soybean 

 plant showed, respectively, i.n per cent of magnesium as against 

 0.88 per cent magnesium. 



All varieties of the seed used contained more magnesium than cal- 

 cium, while ordinarily the remainder of the plant contained more cal- 

 cium than magnesium. This conforms with the data of Schulze and 

 Godet, who report more calcium in the husk and more magnesium in 

 the seed. 



Nitrogen was applied to the legumes as well as to the cereals, so as 

 to be sure that this was not the limiting factor. 



In a number of instances the differences in the yields between dupli- 

 cates were as great as between the different treatments. At several 

 periods during the growth of the plants parasites -caused injuries, some- 

 times great enough to necessitate harvesting the crop. 



CONCLUSIONS 



(1) Wheat, soybeans, alfalfa, and cowpeas grew normally either in 

 96 per cent of dolomite and 4 per cent sand, 100 per cent of magnesian 

 limestone, or in sand containing 7 per cent of magnesite. 



(2) Dolomite up to 40 per cent proved beneficial to plant growth. 

 These results indicate that dolomite and magnesian limestone will not 

 be detrimental as applied in agricultural practices. 



(3) Applications of prepared magnesium carbonate up to 0.7 per cent 

 caused no injury in brown silt loam, but 0.35 per cent prevented the 

 growth of all plants tested in sand. 



(4) The crop yields and the ratio of calcium to magnesium- in the 

 plants bear no direct relation to the ratio in the natural carbonates 

 applied. 



(5) Different ratios of calcium to magnesium within rather wide 

 limits produced no marked differences in yields. 



(6) Increasing the size of applications increased the calcium and 

 magnesium content of plants. 



(7) A tolerance of calcium and magnesium occurred in all varieties 

 of plants grown. With approximately identical yields, wheat straw 



