*. 
tg1r] SHULL—OXYGEN MINIMUM AND GERMINATION 463 
tion, and to determine the influence of temperature, pressure, and 
after-ripening on that minimum. Since the first of these determi- 
nations is that on which the others bear, that portion of the work 
will be considered immediately. 
THE MINIMUM OXYGEN PRESSURE 
The tabulated results of these experiments are given in the 
preliminary report, but for convenience they are presented here 
again, with one addition, a test with X. glabratum (all others are 
X. pennsylvanicum) at 85 mm., and with correction of the oxygen 
pressure for aqueous vapor. 
TABLE I 
DURATION OF EXPERIMENTS IO DAYS 
PERCENTAGE GROWTH IN “arts OF 
A ai “a GERMINATION HYPOCOTYL (MM. 
grou ous. | PHERic —— TEMPERA- 
PRES- = TURE 
ee ee ome | | a ele Petal by eT ele 
mer | oe FL Ri eis £1 TRIS 
a1 0O)) bie khe to ele 
99..... 16.4 | 82.6 | 17.3 9-22 |75.0/100 |45 | 95/14.5 | 30-0 | 4.9/23.3 
90..... 3 | 73-7 | 15-4. | 21-22.680.0) 95 [50 |100/22.8 | 45.9 | 4.3/37-8 
eG 6.25] 68.75) 14.39) 21.5 (56.6) 93.3/23.3/100)42.8 |103.64/10. 5194.9 
72* 16.14} 55.86] 11.69} 20-28 (45.0/100 |20 |10011.5 | 46.0 | 9.4/33.6 
(ee 16.14) 55.86] 11. 20-22 |30.0| 95 | © |100 6.36) 28.5 | 0.0)/22.0 
28*....| 15.27| 12.73| 2.66|21.5-24.5) 0.o|100 | oO | g5| 0.0 | 37.8 | 0.0/28.8 
* Temperature not controlled. 
The table shows at once that there is a marked difference between 
the upper and lower seeds in percentage of germination and amount 
of growth under identical conditions, this difference being the 
expression of a decided difference in the oxygen need of the two seeds 
for germination. The difference in percentage of germination at 
each pressure and temperature used is fairly constant, the lowers 
germinating about 30 per cent more seeds than the uppers in each 
experiment. The difference in the oxygen need is several milli- 
meters, the lowers requiring less oxygen than the uppers for the 
initiation of activity. The oxygen minimum for the uppers is 
approximately 12 mm., at 21° C., while the minimum for the 
lowers is about 9.5 mm. 
It is important to notice the relation which this physiological 
difference in the embryos of the two seeds bears to the difference 
