1916] SHULL—SOILS 19 
When the soil moisture reaches 6 per cent above air-dry, the 
moisture intake by seeds indicates a force equivalent to 4M. NaCl 
solution, which is estimated to exceed 130 atmospheres. At 11 
per cent above air-dry the holding power of the soil has fallen to 
22.5 atmospheres approximately. 
In this manner, comparing the percentage intake from the soil 
with that from the solutions, as given in table ITI, one may estimate 
the surface force for any given moisture content of the soil, each 
soil type, of course, having specific relations. If it were possible 
to make absolutely accurate determinations for several points in 
the curve of moisture intake by seeds, as related to the curve of 
moisture increase in a particular soil, it would be a simple mathe- 
matical problem to calculate the exact water-holding power of 
the soil —— at any soil moisture content whatsoever for 
that soil. 
2. The no. iio sand.—By preliminary tests ranging from 17.5 
per cent to 1 per cent of moisture it was found that there was no 
significant water-holding power in this sand until the moisture 
content fell to less than 2 per cent. At 1 per cent of soil moisture 
the seeds took in over 45 per cent of their own dry weight. 
The results of a series of tests running from air-dry (0.14 per 
cent) to a little beyond the wilting coefficient (1.3 per cent) are 
shown in table VII. 
TABLE VII 
RELATION OF MOISTURE IN NO. 2/0 QUARTZ SAND 
TO MOISTURE INTAKE OF Xanthium SEEDS 
Soil H.0 Intake H,O 
in percentage of absolute in ctgpegeen 3 - air-dry 
weight 
‘ 
©, Th AMOEY) ics ec ess we °. 
oe A SCE a mE AI ay +1.407 
; O 20g ck dv cis ivi cea in 5.02 
ee 2 5 Bie RADAR a bra Venice 21,81 
2, a MSOs a arian 33.98 
pe ah yey e ek Sos ok 42.40 
DOR aoe ee ees eis 45.64 
FAO eee a i 47.40 
5 Ge os PS Se Et Tra 52.06 
Cy SG CORE RSS Se eA as 72.85* 
ur seeds — incipient germination, hypocotyls 
comanuns 3mm. lon; 
