Feb., 1922J 
ARNDT — THE GROWTH OF FIELD CORN 
61 
hibited their development relatively less than 0.0002 N in the solution 
cultures, 0.001 N H2SO4 less than 0.0006 N; and 0.0004 ^ of the aluminum 
salts much less than 0.0002 N. In the solution cultures the dry weight was 
used as a criterion of relative root growth. The results, for reasons to be 
C .f^S AS /?-/V yl-C FttJ r-^S F-N F-C AS A-N A-C^ Ft^S H-fV H-C^ MS 
0.009 2, /V. ' 0,00Q4N O.OOOdTV o.ooJN o.ooziv. 
Fig. 6. Relative growth in sand and solution cultures and the effect of plant growth 
upon the H-ion concentration. For notation see figure 4. 
discussed later, were not satisfactory. In this experiment the roots were 
washed free of sand and then compared by the method devised by Free 
('15). A comparison can readily be made by reference to the numbers 
reported. The highest number indicates the best root development. 
Discussion 
It is plainly evident from the experiments described in the preceding 
pages that the effect of any particular salt upon plant growth depends 
largely upon the composition of the solution in which the plants are grown. 
One of the best examples is the difference in the availability of the iron in 
ferric phosphate in solutions "A" and ''H." Something in solution "A" 
prevents the plant from absorbing the iron. This is not due to any in- 
herent property of the ferric phosphate. At the time series 2 of experiment 
4 was run, plants were grown in a modified solution ''H." The calcium 
phosphate was replaced by an equivalent molecular weight of ferric phos- 
phate. The growth of the tops in these cultures relative to the control 
was 95 percent; of the roots, 68 percent, and the transpiration was 96 per- 
cent. The plants were as well developed as those of the controls. The 
lower nodes of these plants did not show any disco fored nodes, such as were 
found when the plants were grown in the solution with this concentration 
