Apr. 1894.] BOTANICAL SOCIETY OF EDINBURGH. 191 



paper are by no means the same ; and any difference 

 in the temperature of the surrounding air, or of near 

 objects, would destroy, if only in a small degree, the 

 equilibrium of temperature in the two vessels, which 

 would affiect the germinative activity of the seeds, and 

 vitiate the absorption observations by unequal expansion 

 or contraction of the enclosed air. 



If the problem be considered in the light of what we 

 already know of the active influence of light on the 

 green parts of plants in the presence of small quantities 

 of carbonic anhydride, one would be inclined to think 

 that light would probably have an apparently retarding 

 effect on the respiratory function of seeds. In this 

 way, — If the seed coats be at all pervious to light, 

 chlorophyll would be developed in the young plumula, 

 and by the action of the light on this substance, in 

 presence of the carbonic anhydride evolved during germina- 

 tion, a portion of the carbonic anhydride would disappear, 

 and the actual quantity produced during germination 

 would be diminished in proportion to the activity of the 

 light. This indirect effect of light could not take place 

 if the carbonic anhydride evolved by the seeds was 

 removed as soon as formed. It will be seen to what 

 extent this idea is confirmed by the test of experiment. 



Method of experiment. — In my first series of experi- 

 ments I made use of an apparatus similar to the one 

 employed in former experiments on germination, and 

 fully described in a previous paper (Chem. Soc. J., Sept. 

 1880). The only modification introduced is in the form 

 of the vessel containing the seeds experimented upon. 

 This consisted of a piece of combustion tube, worked into 

 «=^ the form shown in 



■^ fF" the figure (Fig. 2). 



^ — ■] The internal diameter 



was 13 M.M., and the 

 ^^' "• length, between the 



two bends, 190 m.m. A tube this size will hold about 3 

 grams of barley loosely disposed all along the interior. 

 Two tubes of the kind described were used in each experi- 

 ment, and the rest of the apparatus was in duplicate. 

 The two tubes were placed side by side in a glass trough 



