210 DRY-FARMING 
In a sandy soil a small percentage of water will cause 
better germination than in a clay soil. While dif- 
ferent seeds vary in their power to abstract water 
from soils, yet it seems that for the majority of plants, 
the best percentage of .soil-water for germination 
purposes is that which is in the neighborhood of the © 
maximum field capacity of soils for water, as explained 
in Chapter VII. Bogdanoff has estimated that the 
best amount of water in the soil for germination pur- 
poses is about twice the maximum percentage of hy- 
groscopic water. This would not be far from the 
field-water capacity as described in the preceding 
chapter. 
During the absorption of water, seeds swell consid- 
erably, in many cases from two to three times their 
normal size. This has the very desirable effect of 
crowding the seed walls against the soil particles and 
thus, by establishing more points of contact, en- 
abling the seed to absorb moisture with greater 
facility. As seeds begin to absorb water, heat is also 
produced. Im many cases the temperature sur- 
rounding the seeds is increased one degree on the 
Centigrade scale by the mere process of water ab- 
sorption. This favors rapid germination. More- 
over, the fertility of the soil has a direct influence 
upon germination. In fertile soils the germination 
is more rapid and more complete than in infertile 
soils. Especially active in favoring direct germina- 
tion are the nitrates, When it is recalled that the 
