Carbon Dioxide in Maturation, etc., of Seeds. 619 



Brown and Escombe (2) have also conducted experiments tending to show 

 the restraining effect of carbon dioxide on growth. Dr. Drabble and 

 Miss Lake in 1905 demonstrated the stimulation effect of small partial 

 pressures of C0 2 , observing that the growth in the length of pea roots 

 was more rapid in 4 per cent. CO2 than in air and than in percentages 

 greater than 7 per cent, of C0 2 . 



Here it will be observed that there are two classes of effects recorded ; an 

 effect of retardation by higher percentages, and an effect of stimulation by 

 lower percentages of CO2. The stimulatory effect of small doses is a general 

 property of narcotic agents. A further series of experiments was therefore 

 arranged to test the effect of C0 2 in various proportions below the inhibitory 

 percentage on the germination and growth of Brassica alba and Hordeum 

 vulgare. The results* obtained with Brassica alba are shown in the following 

 Table. 



Hordeum vulgare gave similar results. 



Table X. — Eesults obtained in Growth of 10 "White Mustard (Brassica alba) 

 Seeds under increased Partial Pressures of C0 2 , showing the Stimulatory 

 Effects of Low Percentages, rising to a Maximum and then declining 

 towards Inhibition. 



Percentage of C0. 2 

 in the atmosphere in 

 each case. 



Increase in 

 weight expressed 

 in percentages 



of original 

 weight of seed. 



Average length 

 of growth at 

 termination of 



experiment 

 in centimetres. 







23 3 



3-8 



2 



16 



4-0 



3 



34 -0 



4-4 



4 



23 -0 



4-3 



5 



9-0 



3-5 



10 



8-0 



2-0 



(25 per cent. CO., gives 

 complete inhibition) 







This experiment was conducted in a dark room. Average temperature, 16'5°C. 



In the foregoing Table it will be observed that the first effect of carbon 

 dioxide is one of stimulation in low percentages. This increases to a 



* The rate of germination was not increased by the low percentages of C0 2 in this 

 experiment, but as has been shown in the case of beans and peas in Table IX, the actual 

 C0 2 content of the seeds is high and falls from an initially inhibitory value as germination 

 proceeds. We should not expect, therefore, small doses of C0 2 in the atmosphere to have 

 a marked stimulatory effect, if any, upon the rate of germination, though their effect 

 upon growth after the escape of the initial high partial pressures of C0 2 in the seeds is 

 clear. 



VOL. LXXXVII.— B. 3 A 



