Influence of Carbon Dioxide . IV. 
461 
Carbon Dioxide. 
The following experiments deal with the question as to how far the 
degree of secondary dormancy is influenced by the concentration of carbon 
dioxide used during the primary period of inhibition. 
These experiments were conducted in three series : with 20 per cent, 
oxygen present, with 10 per cent, oxygen present, and with o per cent, 
oxygen present. 
Table IV gives the results of the series of experiments with a range 
of carbon dioxide concentrations, 20 per cent, oxygen being present in all 
Table IV. 
Effect of various Partial Pressures of Carbon Dioxide (20 per cent. Oxygen 
present) on the Production of Secondary Dormancy in Seeds of Brassica 
alba. 
50 25 % 
50 50 % 
50 80% 
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46 
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Germination after removal of ^16 
the seeds to air. ^ § | 
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Number of day : — § I ^ 
3 4 5 6 7 8 9 10 
0 1 1 1 2 2 2 2 96 % 
1 6 15 24 30 30 30 34 26% 
o 16 22 26 29 29 29 32 30% 
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Mean temperature of laboratory during inhibition period, i 5 °C. 
cases. The percentage of carbon dioxide used during the primary period 
of inhibition has a marked effect upon the degree of secondary dormancy 
obtained. When high percentages of carbon dioxide are used for the 
production of primary inhibition, the percentage of seeds showing secondary 
dormancy as an c after-effect is small and at the same time a considerable 
percentage of seedlings show injury to the radicle. The optimum treat- 
ment for the production of secondary dormancy in these experiments, in 
which the concentration of oxygen present amounts to 20 per cent., is 
with 25 per cent, carbon dioxide* 
The results of the experiments with a range of Carbon dioxide con- 
centrations and 10 per cent, oxygen present in all cases (Table V) are of 
a similar nature. Following the treatment with the higher percentages 
of carbon dioxide injury occurs and the number of seeds showing secondary 
dormancy is small. Both the maximum c after -effect of secondary dormancy 
(73 per cent.) and the minimum percentage of injury (2 per cent.) occur in 
these experiments after treatment with 10 per cent, carbon dioxide. 
I i 2 
