Apr. 1894.] BOTANICAL SOCIETY OF EDINBURGH. 189 



In 1880, Dr. A. Pauchon published a memoir (Role de 

 la Lumiere dans la Germination) in which he criticises 

 closely all foregoing experiments on the subject, showing 

 their defects. He performed many experiments, with 

 proper precautions, but judging of the germinative progress 

 in the way above mentioned, in order to show that only 

 doubtful results could be so obtained. He then suggests, 

 as a measure of germinative progress, the amount of oxygen 

 absorbed by the seeds during germination. This method is 

 a decided improvement, since it substitutes a precise and 

 easily observed measurement, for a rough estimation by 

 which an approximate result can hardly be arrived at even 

 with much trouble. 



Dr. Pauchon's apparatus consisted of two wide tubes of 

 glass, one of which was covered with folds of black paper 

 to exclude light, the other being left clear. The two tubes 

 were placed upright, side by side, during an experiment, 

 the lower ends being closed by corks pushed in to a certain 

 distance. Above the cork in each tube was placed a small 

 vessel containing concentrated potassa solution, and above 





KHO 

 CcnJi. 



, ■- ■ >. this was supported another vessel contain- 



^ \ ing a pad of cotton wool saturated with 



water, on which the seeds were placed, A 

 narrow tube, bent twice at right angles, 

 issued from the upper end of each of the 

 two wide tubes, and its open extremity was 

 immersed in mercury. The limb of the 

 narrow tube, above the mercury, was grad- 

 uated into cubic centimetres and parts of a 

 cubic centimetre, and the absorption in each 

 ^^' ■ tube was observed by the movement of the 



mercury column. Fig. 1 gives the appearance of one of 

 the tubes as fitted up. 



The seeds absorbed oxygen and exhaled carbonic anhy- 

 dride, which was at once fixed by the solution of potassa, 

 producing a partial vacuum ; the mercury then rose in the 

 narrow tube, and the absorption of oxygen was measured 

 by taking an observation and making proper allowance for 

 temperature, pressure, and tension of aqueous vapour, and 

 the volume of the solid and liquid contents of each appar- 

 atus. An account was also taken of the visible progress 



