820 
Journal of Agricultural Research 
Vol. XXIII, No. io 
large quantities the intensity of the action of the metal ions seemed to 
be inhibited during the time usually required in the experiments for the 
aluminum and iron ions to become injurious. 
These injection experiments have their shortcomings. The salts 
absorbed naturally by the plants, as well as the quantity of water, are 
unknown quantities. For this reason the concentration of the specific 
ions after injection into the plant could not be approximated. The 
resultant effects of introducing definite quantities of solutes irrespective 
of their dilution were studied. By this means the cumulative toxicity 
of specific aluminum and iron ions was definitely proved, although the 
toxic and lethal concentration within the stalks are unknown. Probably 
the aluminum and iron ratio to the green weight of the plants offers the 
best basis for comparison, but this must be definitely established. With 
a large quantity of available metals during the seedling stage the ratio 
would be very high, but with rapid growth of the plants under favorable 
meteorological conditions and abundant nitrates the ratio may be kept 
relatively low until later in the life of the plant. Furthermore, different 
plants will absorb the metals at different rates, and this absorption-rate 
capacity of the plants also complicates the problem. 
The brownish-purple discolorations and frequent disintegrations of the 
nodal tissues are the result of the metal accumulations in these tissues. 
Because of the soil relations which have just been described, it seems 
reasonable to conclude that when the accumulations of metal, especially 
aluminum, occur in abundance in the com plants, the soil is deficient in 
available phosphates. Furthermore, under these conditions if the 
organisms commonly found in rotted roots, such as Fusarium moniliforme, 
Trichoderma sp., Rhizopus spp., Penicillium spp., a white bacterium, and 
others, are present in the soil they will produce definite rot lesions in the 
roots and basal parts of the stalks. The condition of the tissues within 
the plants seems to determine the rate of development and consequent 
injuriousness of these rots. 
Resistance to the rootrots in com plants seems to be defined (i) by 
the respective abilities (inherited) of the plants to absorb materials 
present in the soil solution and (2) by the relative concentrations of 
deleterious ions presented to the roots in the soil solution. 
In this consideration of the rootrots of corn it should be borne in mind 
that the importance of using seed which has not been damaged by 
infection by fungi and bacteria is in no way diminished. The value of 
using seed which has not been weakened by infections has already been 
indicated (n, 12 , 13). These investigations cover those effects upon 
plants which occur irrespective of the seed infections and which are 
more directly referable to the soil influences upon the growth of the 
plants and their relative resistances to these influences which determine 
susceptibility to and the extent of development of the rots in the plant 
parts. If these infections can be controlled in a large measure by soil 
treatments and by breeding better strains of corn, the practical impor¬ 
tance of these investigations will be established. Therefore, seed ears 
should be selected which are free from infections and brownish purple 
discolorations of the shank tissues. Moreover, the plants in the field 
which do not show accumulations of large quantities of the metals, as 
evidenced by the nodal plate discolorations and disintegrations of the 
tissues, by the time the ears are matured, are likely to be of greater 
value to the com breeder than those plants which show these character¬ 
istics when grown under similar conditions. These statements apply 
