590 Journal of Agricultural Research vol. vi, no. 16 



calcium and magnesium. Some treatments showed as much as 52.5 

 pounds of calcium and 12.98 pounds of magnesium per ton of dry alfalfa. 

 However, the above amounts were in excess of the absolute requirements, 

 as smaller applications gave as large yields and the alfalfa contained only 

 28 pounds of calcium and 8 pounds of magnesium per ton of dry matter. 

 On this basis 6 tons of alfalfa with a high-calcium content would contain 

 315 pounds of calcium and 77.88 pounds of magnesium, or the equiva- 

 lent of 787.5 pounds of calcium carbonate and 272.5 pounds of magnesium 

 carbonate. Wheat straw, when grown in pure dolomite, contained 14.48 

 pounds of calcium and 14.6 pounds of magnesium per ton, whereas when 

 grown in the absence of excessive amounts of these two elements the 

 straw contained only 5.96 pounds of calcium and 5.43 pounds of magne- 

 sium per ton. 



REVIEW OF THE LITERATURE 



Solution cultures and pot cultures have contributed largely to our pres- 

 ent knowledge of plant nutrition. Woodward (42) found that the solid 

 particles of the soil furnished nourishment to the growing plants and that 

 water acted only as a carrier. 



Wolf (4) found by using beans and maize in controlled solutions, that 

 the concentration as well as the kind of salts in the solution effected 

 plant growth. His results show that when the concentration of the 

 external solution was more than 0.25 per cent it became the controlling 

 factor; whereas if less than 0.25 per cent absorption was controlled by 

 the solution within the roots. 



Dassonville (1) found that cutinization and lignification of the epidermis 

 of leaves occurred much more rapidly in distilled water than in nutrient 

 solutions ; also that the growth of hemp and buckwheat was not influenced 

 by the presence or absence or calcium and magnesium. 



The crop is the measure of the resultant of all factors. In accordance 

 with the present knowledge any one or many of the factors can be con- 

 trolled. Likewise, the total amounts of the elements essential for crop 

 production can be quantitatively determined. 



Magnesium is essential for the growth of any living cell. Calcium 

 is likewise essential except for the lower fungi and lower algae, which 

 alone are able to exist without it. Loew (16, p. 44) shows that neutral 

 oxalates are not poisonous to the lower fungi. He attributes the dele- 

 terious effects in higher plants to the change in the structure of the cal- 

 cium-protein compounds, due to the formation of calcium oxalate, while 

 the disturbance is brought about by the change in imbibition caused by 

 the formation of potassium-protein compounds, and that magnesium 

 may bring about this change provided there is a deficiency in calcium. 



Reed (29) found calcium to be necessary to the activity and growth of 

 chlorophyll-containing organs. Willstatter (40) has pursued in detail 



