610 Mr. F. Kidd. TJie Controlling Influence of 



exemplified in the natural inhibition of maturing seeds in the ovary, and 

 the artificial prolongation of the dormant life of seeds which cannot survive 

 naturally unless germination occui's soon after ripening. 



Section I. — The Relation to Temperahire of the Inhibitory Effect of Carbon 



Dioxide on Germination. 



A large number of experiments were conducted to determine this rela- 

 tion. Brassica alba seeds were used. The result would appear to establish 

 the conclusion that at low temperatures inhibition is caused by very small 

 pressures of CO2, while conversely at high temperatures high pressures of 

 CO2 are necessary to maintain continued dormancy. It would seem 

 probable that this relation to temperature is significant in natural seasonal 

 conditions. The technique in these experiments was the same as before 

 described, the details of each experiment in full are unnecessary and a 

 summary of the results obtained is given. The usual retardation effects 

 were observed throughout, but the numbers in the table indicate only the 

 final total germination out of 20 seeds. 



Table I. — Total Number of Germinations with 20 Brassica alba Seeds in 

 various Percentages of CO2 in Air at different Temperatures. Compiled 

 from 43 experiments. 









2 



4 



6 



9 



12 



15 



18 



24 



30 



36 



42 



3° C. 



18 



2 

























7° 



20 







1 





















10° 



19 







18 



16 



5 

















17° 



20 



20 



20 



20 



18 



12 



3 



2 













20° 



20 



20 



20 



20 



20 



20 





17 



4 



3 



2 







25' 



20 



20 



20 



20 



20 



20 



20 



20 



19 



19 



14 



7 



The temperatures 10° C, 20° C, and 25° C. were maintained accurately within a variation of 

 0'5° C. The temperature of 3° C. obtained with melting ice varied to the extent of 1° C. The 

 other two, 7° and 17° C, are averages of outdoor and indoor winter temperatures. The experi- 

 ments were continued till no more seeds germinated. 



It is necessary to consider the possibility of these results being due not 

 to a decrease with rising temperature in the effectiveness of pressures of 

 CO2 in causing inhibition, but to an increase of oxygen stimulus caused 

 by an increased permeability of the testa under the action of higher 

 temperatures. 



The following series of experiments were therefore conducted with 

 Brassica alba seeds from which the testas had been carefully removed. 

 In these experiments with bare embryos, it was difficult in the early 



