New YorK AGRICULTURAL EXPERIMENT STATION. 485 
F.), and are mostly below .50° C. (1° F.), but during different 
parts of the day they may rise to 2.2 to 2.5° C. (4 to 4.5° F.), 
at 4 inches depth.” 
Criticisms of the data may be made and these we hasten to 
anticipate. It is possible that the differences between the 
tilled and the sodded plats would be reversed at night, as the 
tilled soil probably would lose more heat by radiation and 
diffusion. Such differences, we think, would be more than 
offset by temperatures taken at the hottest part of the day. 
The table, it is now seen, is defective in not having midday 
and midnight observations. An examination of the data shows 
that on some days the differences are large, on others small and 
on still others they are reversed. These variations may be due 
to differences in the air temperature which, when high, would 
give a high tilled-soil temperature; sunshine would cause a 
similar rise in the heat of the tilled soil; dry air would cause 
great evaporation from the grass and a consequent low tem- 
perature beneath it; and windiness might affect the readings 
one way or the other. 
How important this difference in temperature is, cannot be 
said with our present knowledge on the subject. But a con- 
sideration of the ways in which a high temperature influences 
vegetable growth will lead to the conclusion that even a slight 
increase in temperature may be helpful to the apple. King” 
gives the following ways in which a high soil temperature aids 
in plant growth: Heat hastens the solution of food substances; . 
it makes the diffusion of dissolved substances more rapid; it is 
more conducive to rapid and thorough soil ventilation; it de- 
velops stronger osmotic pressure thereby forcing the soil solu- 
tions into the roots and upward mre rapidly; and lastly it 
hastens the formation of nitrates. As regards the formation 
of nitrates King says:'® “In studying the conditions under 
which the nitric ferment works most vigorously, it has been 
learned that the germs cease to develop nitric acid from humus 


1% The Soil. By F. H. King. New York: 1895, pp. 221-225. 
*Tb., p. 224. 
