Apu. 1894.] BOTA^•ICAL SOCIETY OF EDINBURGH. 195 



of l'7o per cent, on the mean of the total quantity of 

 carbonic anhydride produced. 



Of the seven double experiments, six show an increase 

 in respiration in favour of obscurity, and one only in favour 

 of lio-ht. 



Out of the . twenty-one separate observations made during 

 the course of these experiments, fifteen show the greatest 

 activity in obscurity, and the remaining six point to light 

 as being a stimulating agent. I must remark here that 

 two of the observations recorded in experiment 4b, and 

 marked with an asterisk, are probably vitiated by a leakage 

 which was found at one of the joints in apparatus, which 

 would have the effect of diminishing somewhat the current 

 of air which passed over the germinating barley, and the 

 quantity of carbonic anhydride collected would be lessened 

 in consequence. 



Though, as a rule, there appears to be more carbonic 

 anhydride evolved in darkness during germination, yet the 

 increase, as shown by the foregoing experiments, is ex- 

 ceedingly variable in amount, and is altogether so slight 

 that it is more than doubtful whether one is justified in 

 taking the arithmetical mean of so few as seven experi- 

 ments to express the truth. That identity in the con- 

 ditions of moisture and temperature were secured in each 

 double experiment can hardly be doubted. The only source 

 of variation which remains is the difference in the samples 

 of barley and in the constitution of individual corns, a 

 difference which it is impossible to detect, much more to 

 avoid. This difference in the samples of barley used, if 

 not great, say about equal in effect at the most, to the 

 retarding influence of light would in some experiments 

 exaggerate the results in favour of obscurity and in others 

 tend to neutralise them altogether, the results varying with 

 the degree of difference between the samples of barley. 



At the end of each experiment the corns were all care- 

 fully examined. I did not meet with any still or dead 

 corns during all the experiments. There was little or no 

 difference in the outward appearance of two samples, one 

 grown in darkness and the other in strong diffused light, 

 at the end of ten days ; but on dissecting the corns it was 

 found that while the interior of the primitive sheath of the 



