Carbon Dioxide in Maturation, etc., of Seeds. 611 



stages to tell by eye whether germination had begun or not. The bare 

 embryos in the first stages of germination could not be differentiated, but 

 had to be described as either all germinating or all not germinating. In 

 order to bring the results given in the following Table more into relation 

 with those formerly obtained, small figures have been inserted to express 

 the relative condition of growth at the end of the experiment, and the 

 •delay in germination as compared with the controls. 



Table II. — Total Number of Germinations with 20 Bare Embryos of Brassica 

 alba Seeds in various Percentages of CO2 at different Temperatures. 

 Compiled from 14 experiments. 





Control 

 



5 



10 



20 



30 



40 



50 



5°C. 



20 



16 



8 











16 



20 



20 1(! 



20,., 



20 8 



20 4 







20 



20 



20 18 



20 16 



20 12 



20 8 



20 4 





Ten per cent, of oxygen was present in each case. Tke temperatures 16° C. and 20° C. were 

 maintained accurately within a variation of 0'5° C. In the case of the experiments at 5° C. 

 the temperature was less accurately controlled, being obtained by melting ice. 



It will be seen from the foregoing Tables that a rise of temperature of 

 10° C. necessitates roughly the presence of three times as high a partial 

 pressure of CO2 to cause inhibition. Thus in Table I at 10° C. no 

 germinations occurred with C0 2 pressures above 12 per cent., while at 

 20° C. germinations occur up to 36 per cent. Similarly at 7° C. no 

 germinations occur above 6 per cent., while at 17° C. germination pro- 

 ceeds with pressures up to 18 per cent. It must be remembered that the 

 actual partial pressures of CO2 in the tissues of the embryos is probably 

 higher, especially where the testa remains intact, than the values 

 expressed in the tables for the partial pressures of C0 2 in the atmospheres 

 used. 



The result of this series of experiments, both with whole seeds and with 

 bare embryos, thus clearly indicates that a rise in temperature necessitates 

 an increase in the amount of CO2 necessary to produce inhibition in the seeds 

 of Brassica alba. Conversely, a fall in temperature reduces the necessary 

 amount of CO2 to cause inhibition. 



This relation of carbon dioxide inhibition to temperature may be 

 emphasised. In the case of drugs acting chemically on the protoplasm 

 the expectation is that their action will be more effective at high than 

 at low temperatures. Here with carbon dioxide the reverse result has been 



