1911] SHULL—OXYGEN MINIMUM AND GERMINATION 461 
Any increase of the aqueous vapor about the seeds was invariably 
attended by a marked decrease in the percentage of germination 
and amount of growth, due to the fact that such increase necessa- 
rily reduces the oxygen supply of the germinating seeds. In spite 
of the rapid evaporation and removal of the water, there is suf- 
ficient moisture present to bring about all the growth changes 
which the oxygen supply will permit, as was shown by repeated 
tests. 
In correcting the pressures for water vapor, the only practicable 
method is to measure directly the amount of dry air passing into the 
apparatus per hour, and the amount of water vapor drawn from it 
in the same length of time, then calculate the proportion of each 
gas in the gram molecular volume. A concrete example will make 
the method clear. At 88 mm. pressure, 30° C., the dry air drawn 
through the apparatus measured at 20° C., barometer 745 mm., is 
4.37 liters per hour. Reducing this volume to standard tempera- 
ture and pressure gives 3.9 liters. This volume is 0.178 of the 
molar volume. The amount of water vapor present with that 
amount of air drawn from the apparatus as determined by phos- 
Phorus pentoxide absorption was 1.65 grams per hour; and this 
amount is readily found to be 0.086 of the molar volume. The 
dry air and water vapor together amount to 0.264 of a mole per 
hour. The pressure recorded by the manometer is 88 mm. Of 
this amount, 178/264 (59.3 mm.) is air pressure, 86/264 (28.7 mm.) 
aqueous pressure. The oxygen pressure is then readily obtained, as 
oxygen constitutes 20.93 per cent of the atmosphere. The correc- 
tions were made on the basis of the average of three determinations, 
and are therefore fairly reliable. 
To determine whether reduction of pressure per se has any 
effect on germination, hydrogen gas with a low oxygen content 
was admitted to the chambers containing the seeds. The hydro- 
gen was imported by the Linde Air Products Co., of Buffalo, N.Y., 
and was found to contain 2.34 to 4.7 per cent of oxygen. The 
gas with more than 2.5 per cent of oxygen was of little use, because 
the oxygen pressure was so high that no comparison with the 
reduced pressure experiments could be made. This hydrogen was 
under 120 atmospheres of pressure, but was controlled by high 
