SOILS OF MASSACHUSETTS AND CONNECTICUT. 45 
It becomes evident then, that the capacity of a subsoil to furnish 
capillary or usable moisture to crops depends, under average condi- 
tions, primarily on the natural character of the subsoil itself, i. e., on 
the size of the soil grains, and that it is practically independent of the 
supply of humus. The supply of humus in the surface soil, on the 
other hand, greatly lessens the loss from evaporation and increases 
the moisture-holding capacity, both as referred to the rise of the 
capillary water and to light rainfall. Below the depth of a foot, 
moreover, surface heat penetrates very slowly. Hence, it is reason- 
able to suppose, in want of definite experimental data to prove the 
point, that the water-holding capacity of the subsoil, as determined 
chiefly by its texture, has an important bearing on the temperatures 
surrounding the roots of trees and plants. It is to be regretted 
that accurate experimental data are not available on this subject. The 
extensive series of observations upon soil temperatures at different 
depths, carried out in different parts of the United States and in 
foreign countries, have neglected to take account of the moisture 
content of the soil at various depths where the temperatures were 
measured. It is a well-observed fact, however, that in irrigated 
orchards any overirrigation prevents good color on either apples or 
peaches. 
Dr. D. T. MacDougal, in his research work for the Carnegie In- 
stitution, of Washington (1908), concludes that. — 
The facts disclosed as to the actual temperatures in the soil, the diurnal and 
seasonable changes therein, lead to the belief that the differences in tempera- 
ture of the aerial and underground portions of plants can not fail to be of very- 
great importance in the physical and chemical processes upon which growth, 
cell division, nutrition, and propagation depend. 
Desert soils have a low humus content, and, consequently, they 
offer excellent opportunity to observe the effects of variation in 
texture and structure of the mineral particles themselves. Eliminat- 
ing soils influenced by alkali, Dr. MacDougal remarks : 
On all other soils in which clay, loam, sand, or rocks predominate the fea- 
ture which has the greatest determining influence (on adaptation to plants) 
is that of the amount and disposition of the moisture. Many striking disposi- 
tions of the root systems are being discovered which can only be correlated 
with the moisture factor. 
E. S. Goff 1 adduces observations to show that the temperature of 
the water at the time it enters into the roots from the soil has some 
relation to the temperature of the stem of the plant for a short dis- 
tance above the surface soil, and that the distance up the stem to 
which this temperature is felt depends upon the rapidity of the flow 
1 Agr. Sci., Vol. I, p. 134, Bui. 36, U. S. Weather Bureau. 
