Carbon Dioxide in Maturation, etc., of Seeds. 613 



Table III. — The Effect of Decreased Partial Pressures of Oxygen on Carbon 

 Dioxide Inhibition in Brassica alba Seeds. Small amounts of C0 2 are 

 sufficient to cause inhibition if little oxygen is present. 



Atmosphere of oxygen, carbon dioxide, and 

 nitrogen. 



Germinations out of 

 20 seeds while in artificial 

 atmospheres. 



Proportion of 

 remainder which 

 finally germinated 

 on removal to air. 



Oxygen percentages. 



Carbon dioxide 

 percentages. 



2nd 

 day. 



3rd 

 day. 



4th 

 day. 



5th 

 day. 



per cent. 

 21 (air) 



per cent. 

 (air) 



18 



20 



20 



20 





8 

 8 

 8 

 8 





 1 



3 

 6 



13 



13 

 15 



18 

 19 

 15 

 12 



18 

 19 

 18 

 13 



20 

 20 

 20 

 16 



All 



4 

 4 

 4 





 1 



6 



6 



18 

 1 



18 

 1 



19 



3 

 



All 

 All 

 All 



Average temperature, 14° C. 



It will be noticed from the preceding Table that the effect of decreasing 

 the oxygen supply is to intensify the inhibitory action of carbon dioxide. 

 Thus, with a decrease of oxygen to 8 per cent., the inhibitory effect produced 

 by 6 per cent, of carbon dioxide is very marked. With a decrease of oxygen 

 in the atmosphere to 4 per cent., complete inhibition is produced by 6 per 

 cent, of carbon dioxide. 



Here again it must be remarked that this relation may very likely be 

 significant in many cases of delayed germination under the influence of C0 2 

 in natural conditions. 



Table IV. — Effect of various Partial Pressures of Oxygen on the C0 2 

 Inhibition of Germination in Brassica alba Seeds. Total number of 



germinations obtained out of 20 seeds. 



Percentages of C0 3 







9 



12 



15 



18 



21 



24 



27 



30 



Oxygen 5 per cent 



20 



6 



4 



























„ 10 „ 



20 



18 



17 



10 



3 



1 















„ 15 „ 



20 



20 



20 



15 



10 



2 















„ 20 „ 



20 



20 



20 



18 



12 





3 











„ 30 „ 



20 



20 



20 



20 





11 



5 



2 



1 



Average temperature 16"7°C. ; extremes 13-18° C. The atmospheric residuum is N 2 in these 



experiments. 



