146 - AGRICULTURAL REPORT. 
est to it, and the sands absorb least. Fertile earths absorb more than 
those poorer in humus and clay. The included air, standing over them, 
at last becomes so void of oxygen, that lights are extinguished, and ani- 
mals die in it. 
3. The methods of absorption differ; humus combines partly with the 
oxygen, chemically; the inorganic earths absorb the gas without inti- 
mate combination. 
4, When earths are frozen or covered with an icy surface, absorption 
of oxygen ceases; and the action increases with the warmth of temper- 
ature, varying from 59° to 653° F. Many phenomena prove that oxygen 
is an important agent in vegetable as well as in animal economy. It is 
particularly necessary to the germination of seeds and the growth of 
plants. By turning up the soil in any manner fresh layers are brought 
into contact with and fertilized by the oxygen, and as a moist condition 
of soil favors this absorption, it should be preserved. 
Power of the earths to vetain heat.—The earths have the power of re- 
taining the warmth which they accuinulate from the atmosphere and the 
heat of the sun, and of giving it out to surrounding bodies. Itis different 
from specific heat, and its degree depends upon the capacity of the body 
for conducting heat. 
1. The sands possess this power to the greatest extent; hence the 
heat and dryness of sandy districts in summer. Their slight water- 
coutaining power, in consequence of which little warmth is lost by evap- 
oration, increases this condition. 
2. Slaty marl stands next to sand in this capacity; and this, joined to 
its greater power of retaining water, contributes largely to its fertility. 
3. Humus has the least power of retaining beat, and turf soils abound- 
ing in humas warm but slowly, because they contain water, only a small 
portion of which they lose rapidly by evaporation. 
4, Magnesia, combined with sands and slaty marls, largely possesses 
this heat-retaining power. 
5. The greator the mass of an earth the more extensive will be its 
power of retaining heat. We may, therefore, from the absolute weight 
of an earth conclude tolerably well in regard to the extent of its power. 
Warming of soils by the sun.—The various earths acquire heat from the 
sun in different proportions, and this property may exert a sensible 
influence on vegetation. -Land eonsisting of light-colored clay warms 
less quickly and powerfully in the sunlight than a dark, dry Soil; black 
garden-mold, rich in humus, becomes much warmer than meager lime- 
stone or clay soils. Very different external circumstances may affect 
the warming of the soils, and may be classed as follows: 1st, the different 
colors of the surface earths; 2d, the different degrees of dampness present 
- during the exposure of the earths to the sun’s influence; 3d, the compo- 
nent materials of the earths; 4th, the different angles at which the sun’s 
rays fall upon the soil. ; 
1. The’intluence of the eolor of soils on the quantity of heat received 
by them may be tested as follows: Place thermometers in the several 
soils, covering their bulbs an eighth of an inch high with earth; sprinkle 
the surfaces, by means of a fine-lawn sieve, with lampblack for a black 
color, and magnesia for a white, leaving one soil of.its natural color. 
In August, with a temperature in the shade of 77° F., the increase with 
the black color was found by Professor Schiibler, of the University of 
Tiibingen, to be from 77° to 1234° F.; the white from 77° to 110° F.; 
and the natural color from 77° to 112459 F. Thus, the increase of tem- 
perature with the black-colored earth was 464°; with the white, 33°; 
and with the natural, 354°. Other colored earths exhibit corresponding 
