Feb., 1922] 
ARNDT THE GROWTH OF FIELD CORN 
63 
not at all proportional to the increase in concentration. The effect on the 
development of the roots is more nearly related to the concentration. This 
difference in root development is much greater than is actually indicated 
by the small differences in the relative root yields. The development of 
the small secondary roots is inhibited at the higher concentrations; but 
coinciding with the stunting of the secondary roots there is a thickening 
of the main roots and an increased formation of prop roots, which increases 
the weight of the root system. Because of this fact, the dry weight is a 
poor criterion of the root development and of the number of feeding roots. 
In the solution cultures, the roots were barely able to penetrate a solution 
of 0.0006 N, no secondary roots formed, and the root tips were frequently 
swollen and recurved. Nevertheless, the roots were able to absorb sufficient 
material to produce a stunted growth. The poor development of the roots- 
in the higher concentration probably accounts to some extent for the 
tendency of chlorosis to be associated with aluminum injury. It is likely 
that the capacity of aluminum salts to antagonize the action of iron salts, 
as has been noted by Stoklasa ('18&), may be the most important factor. 
The effect of aluminum salts on root development described above 
is similar to that noted by Rothert ('06) in his study of the effect of aluminum 
chloride and sulphate upon the growth of Zea mays. He states that the 
shoots suffer the least and the secondary roots the most. A i percent 
solution was necessary to depress growth in Knop's solution, which is 
many times the concentration necessary to depress growth in solution 
**H." Hartwell and Pember ('18) secured a 44 percent depression of the 
growth of barley with 0.0008 N aluminum sulphate in solution "H." It 
is very likely that this concentration would not produce a much greater 
depression with corn. 
Some interesting suggestions as to the possible cause for this peculiar 
action of aluminum salts may be found in the studies of Stoklasa ('i8a, 
Berthelot and Andre ('95), and Meurer ('08). The latter has shown that 
the amount of aluminum absorbed by slices of beet or carrot roots from a 
solution of one of its salts is independent of the concentration of the salt 
in the solution. Tissue killed by chloroform absorbs the aluminum as 
readily as living tissue. He concludes that aluminum forms some chemical 
compound with the pectic bodies of the middle lamella. The relatively 
lesser toxicity of aluminum salts at increased concentrations has led 
Stoklasa ('18&) to conclude that aluminum combines with the cell wall to 
form colloidal salts. This action renders the cell less permeable. The 
researches of Sziics ('12) demonstrated that it also acts on the protoplasm 
and causes it to set. The singular thickening of the main roots of the 
plants grown in the solution cultures is probably due to some unique action 
of the aluminum upon the tissues of the root. Berthelot and Andre grew 
plants in pot cultures to which aluminum salts were added. In all the 
plants grown in their cultures, aluminum oxide formed a much larger 
