ToII] SHULL—OXYGEN MINIMUM AND GERMINATION 469 
alone, or does the difference in pressure as such have a part in pro- 
ducing this effect? Comparison of the results in hydrogen gas 
with those at 90 and 99 mm. in table I, which approach most nearly 
the same oxygen pressure, shows that the difference is probably 
nearly all due to difference in oxygen pressure, rather than to a 
difference in barometric pressure. It is possible that great reduc- 
tion in pressure may affect slightly the percentage of germination 
and the amount of growth. WUIELER (28) came to the conclusion 
that growth is independent of pressure; and SCHAIBLE (25) ob- 
served that reduced pressures increase the rate of growth, but that - 
the influence of air pressure on germination is very slight. 
From the data of table III, as compared with the results of the 
other experiments, it appears that the oxygen minimum is prac- 
tically the same for any given temperature, whether the reduction 
is accomplished by reducing the atmospheric pressure, or by dilu- 
tion with inert gases like hydrogen. 
AFTER-RIPENING OF XANTHIUM 
Several attempts have been made to test the after-ripening of 
Xanthium seeds, with the results here briefly recorded. During 
October and November 1910, I made a test of the germination of 
X. glabratum at normal pressure, average temperature 23° C., at 
Transylvania University. Seeds in three different stages were 
taken as follows: green seeds, so young that the testas were still 
quite white; seeds which had ripened normally on the plants in 
1910; seeds collected in the same locality in 1909. The seeds were 
prepared for germination as in all the other tests, and the integu- 
ments removed carefully. The results show that, at normal pres- 
sures at least, the protoplasm does not pass from an inactive state 
to an ultimately more active one, and that there is no after- 
ripening in that sense. The seeds averaged as follows in growth 
in length: 
Lowers - - Uppers 
IQIO green SCEUS.. 1.2.4. essneees 46.0 mm, 37.0 mm. 
36.0 mm. 31.5 mm 
1910 brown seeds. .....--++++++++- 
1909 brown seeds.......-+-+-++-+:- 34.3 mm. 
One experiment with fresh seeds at reduced pressure agrees with 
these results. The seeds were kept at 90 mm. pressure, tempera- 
