PHYSICAL CHARACTERS OF THE SOIL. 161 
ing roots have in which to expand themselves, and the 
more abundantly are they able to present their absorbent 
surfaces to the supplies which the soil contains. The fine- 
ness of the particles may, however, be excessive. They 
may fit each other so closely as to interfere with the 
growth of the roots, or at least with the sprouting of the 
seed. The soil may be too compact. | 
It will presently appear that other very important prop- 
erties of the soil are more or less related to its state of 
mechanical division. 
§ 3. 
ABSORPTION OF VAPOR OF WATER BY THE SOIL. 
The soil has a power of withdrawing vapor of water 
from the air and condensing the same in its pores. It is, 
in other words, hygroscopic. 
This property of a soil is of the utmost agricultural im- 
portance, because, Ist, it is connected with the permanent 
moisture which is necessary to vegetable existence; and, 
2d, since the absorption of water-vapor to some degree 
determines the absorption of other vapors and gases. 
In the following table we have the results of a series 
of experiments carried out by Schiibler, for the purpose 
of determining the absorptive power of different kinds of 
earths and soils for vapor of water. 
The column of figures gives in thousandths the quantity 
of hygroscopic moisture absorbed in twenty-four hours by 
the previously dried soil from air confined over water, 
and hence nearly saturated with vapor. 
Quartz sand, COaTSC........ 0. cc ccc e cece cece ne eneneras 0 
GYPSUM op cciscds «sings seals eases eee sente s cam aea ee ses 1 
TAU SANG is:o.ir6:5 siaararesarsie aacvarsconas os pate due Vie erernie aia Vinwrelewetyes 3 
Plough. lands: swesme saan seews tw, s vedesaaies vance sees 23 
Clay soil, (60 per cent clay)........... cc cece eee ee eenees 28 
Slaty Marl. edcs cas esreiewesd schacisseisnaacua odessa aie ares o 33 
Loam.....ssessesesecseeees sraieisie wath bia terelete ssl alsjowia siaters «. 3D 
