314 JAMES GEERE DICKSON 
the magnesium-calcium ratio is high enough to exert a toxic efifect 
upon the plant. A deficiency in potassium, however, causes a de- 
crease in the vegetative growth of the oat plant, and also affects the 
total dry weight which in this case is only about one half that of the 
plants grown in the normal solution. A deficiency in phosphorus or in 
nitrogen also causes a very great decrease in vegetative growth. 
There is no very marked difference in this respect between the effects 
of a deficiency in phosphorus and those of a deficiency in nitrogen. 
Table 5 
The Average Yields of Dry Weight by Plants Grown in the Normal Solution and in 
Solutions in Which Certain Essential Nutrients Are Reduced to One Tenth 
the Normal Amount 
No. Det. 
per Year 
Solution, Deficient 
Element Given 
Weight of Dry Matter in Grams 
1915 Crop 
1916 Crop 
1917 Crop 
Ave. 
4 
Normal 
12.41 =b I 
20.90 d= 2 
34-44 ± 0 
22.58 
2 
Mg 0.1 
35-42 ± 3 
2 
Ca 0.1 
13.17 ± I 
23-85 ± 4 
24.74 ± 3 
20.59 
2 
K 0.1 
6.48 ± 3 
15.88 ± 6 
15-99 ± 0 
12.77 
2 
P 0.1 
2.73 ± I 
1.23 ± I 
2.77 ±0 
2.24 
2 
N 0.1 
4.00 =t I 
.41 ± 0 
2.70 dz 0 
2.37 
The comparative effect of a deficiency in the respective nutrient 
elements upon the total dry weight of dry matter is presented graph- 
ically in figure 3. 
The Relation between Nutrients and Grain Production 
Although the total dry weight of the plants grown in the solutions 
deficient in magnesium or in calcium is the same or even greater than 
that of the plants grown in the normal solution, yet the total dry 
weight of the grain produced by the plants grown in the former solu- 
tions is lower than that produced by plants grown in the normal solu- 
tion (table 6). The ratio of grain to straw for the plants grown in 
magnesium- or in calcium-deficient solutions is lower than that of 
plants grown in the normal solutions. The weight of the individual 
kernels of the plants grown in the magnesium- or in the calcium- 
deficient solutions is also below that of the kernels of plants grown in 
the normal solution (table 7). A deficiency in magnesium or in 
calcium, therefore, has a markedly deleterious effect upon the grain 
production of the oat plant. 
