8 BOTANICAL GAZETTE [JULY 
For a comparative study of the moisture relations of seeds and 
soils at the wilting coefficient of the soil, a series of soil samples 
was obtained from Washington, D.C. The necessary data regard- 
ing these soils are given in table IT. 
TABLE II 
ee ie | ete | ee | 
Dee teas Yuma, Arizona Sand 1.35+0.04 | 0.73+0.02 ©. 205 
7 SEDO ae Highmore 
South Dakots am 23.79%90.10 | 12.93+0.05 g.%3 
econo North Platte, Very fine 
Nebraska sandy 
loam 15.330.08 | 8.33+0.08 1.836 
Pe a North Platte, 
Nebraska oam 22.84+0.03 | 12.410.02 2.28 
eae Amarillo, Texas lay | 650.02 | 16.120.01 3.82 
cee North Platte, Neb.| Clayloam}| 30.08+0.04 | 16.34+0.02 5.21 
ae Akron, Colorado | Finesand| 5.90+0.05 | 3.21+0.03 0.75 
So sve. uma, Arizona and I.53=0.01 0.83+0.01 0.218 
Gk Akron, Colorado | Loam I19.Q910.12 | 10.820.06 2.3 
in MMi hava ee 
MetHops.—While the internal forces of Xanthium seeds have 
been approximated by osmotic means, many seeds lack semi- 
permeable coats. For such seeds a vapor pressure method has 
been used which gives results which are in a way comparable to- 
the osmotic measurements. It consists essentially in measuring the 
vapor pressure equilibrium of the air-dry seeds over sulphuric acid 
of varying strength, and calculating the internal pressure of the 
seed from the vapor pressure of the solution over which it was 
found to be in equilibrium. Owing to our slight knowledge of the 
concentrated solutions and of the exact relations of colloids to 
water vapor, the calculations can give only a rough estimate of 
the internal forces of the seeds, but they are near enough to the 
osmotic determinations to be of great interest. 
The sulphuric acid series was chosen with some reference to 
the LANDOLT-BORNSTEIN tables to facilitate calculation. Begin- 
ning with water, the series included 16, 26.5, 35, 39, 50, 54, 57-5» 
66, 73, 84.5, and 96-99 per cent H.SO,. These fluids were placed 
in tightly sealed, small, wide-mouthed bottles. The seeds to be 
