8i8 
Journal of Agricultural Research 
Vol. XXIII, No. to 
and general metabolism. It is known that they act in a beneficial 
manner upon certain tissues when present in very small quantities. 
When the quantities are supra-optimal the effects become pathological. 
The influence of the metals which frequently accumulate in the scutel- 
lum of the kernels, as shown in Plate 5, C, upon germination and growth 
of the seedlings must also be considered. There is some evidence to 
indicate that they affect the amylase activity in these tissues and inhibit 
the growth of the young seedlings. 
Many weakly germinating seedlings have been studied in this regard, 
and it has been found that many seedlings which possess a darkened 
scutellum, such as has been described by Adams and Russell (2), will 
show relatively large quantities of accumulated iron in these tissues in 
comparison with the quantities which normally are present in the seed¬ 
lings of high-yielding, disease-free types. Whether or not these tissues 
are affected by the metals so that they too become more easily invaded 
by fungi has not been determined, yet they frequently are infected by 
Rhizopus nigricans Ehrb., Penicillium spp., and other organisms. 
The conditions of high aluminum availability in acid soils are chiefly 
those which occur when calcium and phosphorus salts are lacking, as 
shown by Mirasol ( 18 ). For this reason the effects of aluminum com¬ 
pounds may rapidly become injurious, due perhaps both to a cumulative 
toxicity in the concentration centers in the plants and to a phosphorus 
starvation of the growing and functioning tissues. 
The influence of nitrates in the soil has already been referred to. 
When they are abundant the plants seem to grow more vigorously and 
the quantity of aluminum compounds may not reach toxic proportions 
in any particular part until the plants have made good vegetative 
growth. When the available nitrates, as well as the calcium and phos¬ 
phorus in the soil, are low, as shown in Plate 4, A and B, and Plate 19, 
the cumulative aluminum toxicity develops rapidly and the growth of 
the plants is retarded. The nodal tissues become disorganized very 
early in the life of the plant. Plants in the condition shown in Plate 
19 have recovered from this stunting effect after heavy rains. New 
roots may push out, provided the basal tissues are not too badly affected, 
and with a decreased percentage of available salts of aluminum and 
iron in the soil more rapid growth may take place. Any retardation of 
the early growth of the stalks due to'any cause, either the accumulated 
metals, infected seed, or insect injury, results in a lessened productive 
capacity of the plant. 
IMPORTANCE OF AVAILABLE PHOSPHATES 
As the quantities of available aluminum compounds vary according to 
the type of the soil and according to the farm management practiced 
upon the different soils, and, furthermore, as the amount of moisture 
affects the quantities of available aluminum compounds, as has been 
shown by Conner (6), it is evident that the rate of absorption of these 
salts must be related to their respective availabilities during different 
periods of the growing season. The other available elements, calcium 
and phosphorus, also vary in quantity in the different soils. The phos¬ 
phorus relation is the most important one in connection with the alumi¬ 
num and iron salt availabilities. The aluminum salts are not available 
in any considerable quantities in a soil containing soluble phosphates. 
It is a recognized fact that most acid soils are deficient in phosphates. 
