3i6 
JAMES GEERE DICKSON 
food translocation and storage is that analyses show an abundance of 
magnesium in the seeds of plants. It has been shown that magnesium 
occurs chemically combined with many of the fats and some of the 
phospho-nitrogen compounds. It is possible, therefore, that the major 
role of magnesium in plant nutrition is in connection with seed forma- 
tion, and if this be true, it is evident that a deficiency in this element 
in the culture solution will affect seed production rather than vegeta- 
tive growth. On the other hand, although calcium apparently plays 
no very important part in the chemical composition of the seed, yet 
when this element is deficient in the culture solution a marked decrease 
results in the amount of grain produced. The decrease in the amount 
of grain produced in calcium-deficient solutions is nearly as great as 
that noted in magnesium-deficient solutions. It would appear, there- 
fore, that calcium does not function directly in the synthesis of carbo- 
hydrates and proteins, but rather as a neutralizer of acids in the plant 
and as a carrier for nitrogen, phosphorus, and sulphur compounds, a 
view first advanced by Holzner (1867) and Schimper (1890), and more 
recently supported by Chirikov (1914) and Robert (191 7). 
Truog (1916) finds that plants with a high protein content generally 
have a high calcium content, and that when manganese phosphate is 
used instead of calcium phosphate as a source of phosphorus the plants 
grown in such a solution have an extraordinarily high manganese 
content. Although neither calcium nor manganese is an important 
constituent of the proteins of the protoplasm, and although neither 
enters into direct chemical combination with any of the more important 
compounds of the seed, yet their presence in plants especially high in 
nitrogen content must indicate some connection with protein forma- 
tion. In the synthesis of proteins organic acids are formed which 
must be neutralized by some base to form relatively insoluble salts; 
calcium, therefore, may be imagined to be the base which chiefly func- 
tions in removing these acids from the field of action. From this 
point of view it would appear that if the nutrient solution is deficient 
in calcium, and if no other base is present which will form insoluble 
salts with the organic acids in sufficient quantity to remove the latter, 
then the normal development of the plant will be disturbed by the 
accumulation of the acids in sufficient quantities to exert a retarding 
effect upon the plant's metabolism. 
The plants grown in the solutions deficient in potassium produce 
only about one half the amount of total dry matter produced by the 
