66 BULLETIN 1059, U. S. DEPARTMENT OE AGEICLLTLEE. 
SOIL MOISTURE AND SOIL QUALITIES. 
The subject of soil moisture is closely related to that of precipita- 
tion. Since the physical and chemical properties of the soil are 
closely linked up with moisture, it seems logical to consider all of 
these subjects together as a question of water supply, after which 
atmospheric conditions which particularly affect water losses may 
be taken up. 
There is practically no question that water is the prime requisite 
of all life, for without water the colloids could not exist. It is 
hardly more true of plants than of animals that, besides possessing 
water at any given time, they must be almost continually given new 
supplies to make up for unavoidable losses ; but. with the exception 
of aquatic species, plants are more at the mercy of the moisture of 
the habitat than are animals, because they can not move to new 
supplies — the water must somehow be brought within their reach. 
Ecologically, it is perhaps unsafe to say that moisture has more 
to do with the establishment, development, and succession of a plant 
society than any other condition, that is. that it controls the char- 
acter of the plant society more directly. It is perhaps nearer the 
truth to say that when the temperature conditions are about optimum 
for a given plant or society, moisture determines success or failure 
almost absolutely. Yet this does not express the situation, for in a 
vast majority of cases the plant society must depend at all stages, 
but particularly at its initiation, upon a proper balance between 
temperature and moisture, especially as these are integrated in the 
condition of the surface soil. 
In the last analysis all other environmental conditions react more 
or less on the soil moisture, and the best measure of their influence in 
this respect is found in a measure of changes in the soil moisture. It 
is readily seen, therefore, that the direct measurement of the soil 
moisture is of the utmost importance. 
The moisture content of the soil, whether expressed in grams per 
kilogram of soil or cubic centimeters per cubic meter of soil, does not 
give directly a measure of the rate at which it may be obtained by the 
plant, because of the great variation in the moisture-withholding 
powers of soils. This rate is obviously very important whenever the 
atmospheric conditions are such as to cause heavy loss from the leaves, 
and may often determine success or failure of the individual plant 
and of the society. 
Osmosis as a Factor in Water Absorption. 
The rate of absorption is unquestionably dependent upon the simple 
physical process known as diffusion, which is commonly called 
osmosis when speaking of plants, since the mixing of the two liquids 
