The Fixation oe Nitrogen. 9 
about twenty inches around the trunk of the tree. No one has 
to my knowledge demonstrated how small an amount of nitrates 
may do injury to an apple tree if placed within reach of its feeding 
roots, especially at the period of its most rapid growth. My ex¬ 
periments were made to see whether this amount would produce 
any effect upon the trees and to observe how this effect expressed 
itself and not with the idea of determining the tolerance of the 
apple tree for this particular salt, sodic nitrate. 
The trees in this orchard, especially the first ones attacked, 
twelve or more in number, did not turn yellow, dwindle and grad¬ 
ually succumb, but, though they were in full leaf and appeared 
vigorous and healthy, the leaves suddenly turned brown and 
drooped and the trees died outright within ten days or a fortnight. 
As the trees in this orchard continued to die throughout the season 
of 1910 it may serve a purpose to calculate the amount of nitrate 
available to an ordinary-sized tree, fifteen years of age. The roots 
of such a tree will occupy an area represented by a circle forty feet 
in diameter, at least; this will give approximately 1,200 square feet 
of surface. All of the feeding root's in this orchard were tound 
to be within two feet of the surface. The sample of soil was 
taken to a depth of two inches or one-sixth of a foot and there 
would be two hundred cubic feet of such dirt to furnish nitrates to 
the tree. Assuming a cubic foot of this sandy soil to weigh ninety 
pounds, we have 18,000 pounds of nitre-rich soil, 11.6 percent of 
which is soluble in water, or 2,088 pounds, four-tenths of which 
(39.97 percent) or 835 pounds consists of sodic nitrate or its equiv¬ 
alent in other nitrates. 
In this calculation I have assumed that the soil below a depth 
of two inches furnished no nitrates—which is altogether contrary 
to the facts. It may, however, serve to convey a clear idea of the 
large amount of nitrates present within the feeding areas of these 
trees, 832 pounds in this case, ready to be moved downward and 
supplied to the feeding roots, all of which a^e within two feet of 
the surface, by a rain or irrigation or any other agent, possibly even 
by cultivation of the soil. This was in May when the trees were 
feeding actively. Our sample taken in August is still worse, 12.8 
percent soluble in water, placing 2,304 pounds of salts above the 
roots of the tree with 1,178 pounds of sodic nitrate or its equivalent. 
When we incorporated five pounds of sodic nitrate with the soil 
about a four-year-old tree and watered it, we injured some of the 
branches; when we incorporated twenty-five pounds and irrigated 
it we killed the tree in four days. It is not probable that every tree 
in this orchard had either 1,178 or even 832 pounds of sodic nitrate 
at its disposal but all of the trees in this area, some eight acres or 
more, died and were dug up between May 1909 and March 1911. 
Another way to convey an idea of the large quantities of nitrates 
