Influence of Carbon Dioxide. IV. 48 £ 
Oxygen. 
Experiments conducted by Crocker (7) [ Xanthium ], Shull (8) [Xan- 
thium\ and by Rose (9) \Datura Wrightii and Martynia sp.] have led 
these authors to conclude that with these seeds the factor limiting 
germination is the low permeability of the testa to oxygen. The results of 
Atwood (10) indicate a similar conclusion with regard to Avena fatua. 
As has been said above, a possible cause of the non-germination of White 
Mustard seeds after treatment with carbon dioxide may be either lack 
of oxygen or excess of carbon dioxide. It has been shown that 
the seed-coats do not appear to change with regard to their permea- 
bility to gases as the result of the treatment which produces secondary 
dormancy. But owing to the alteration in the condition of the embryo, 
already demonstrated, it is quite possible that the normal interference of 
the testa in gaseous interchange may act as a definite factor in the 
maintenance of secondary dormancy. It has been seen that the seeds 
showing secondary dormancy which have been redried are more sensitive 
to carbon dioxide. This increased sensitiveness in all probability exists 
previous to redrying. 
The following experiments were conducted : Inhibited White Mustard 
seeds were placed in concentrations of oxygen up to 100 per cent, at one 
atmosphere pressure. No increase of germinations over the control in air 
resulted, and we may therefore conclude that the failure to germinate 
cannot be attributed to a need of oxygen on the part of the embryo. 
Table XXII. 
Negative Result of Treatment of White Mustard Seeds shozving Secondary 
Dormancy with Increased Concentrations of Oxygen and of Treatment 
to Exposure to a Vacuum. 
Treatment of 
inhibited seeds . 
Control inhibited 
seeds in open flask. 
5° % oxygen. 
50 % nitrogen. 
100 % oxygen. 
Exhausted \ hour ; 
75 mm. Hg 0 2 
pressure admitted 
for two days. 
25 
Number of germinations on removal to air after — 
123456789 10 
day. days, days . days. days. days. days. days. days. days. 
0 3 4 5 5 
00000 
5 5 5 5 
0000 
5 
o 
0000 
1 
0000000 2 2 2 
seeds used in each experiment. 
Mean temperature of laboratory, I5°C. 
To test, on the other hand, the possibility of continued inhibition 
being due to an inhibiting concentration of carbon dioxide in the embryo 
owing to an increased sensitiveness to this gas on the part of the embryo, 
inhibited seeds were submitted to a vacuum for a short period and then 
