426 Baker . — Quantitative Experiments on 
was continued until the two cultures without C 0 2 showed signs of flagging 
(the ones with aldehyde were the first to do so). They may be taken as 
showing conclusively that acetic aldehyde cannot be used by the plant for 
photosynthesis. The plants showed no symptoms of poisoning under acetic 
aldehyde. 
Conclusion from Results. — Acetic aldehyde cannot be used for photo- 
synthesis, though its poisonous action tends to retard respiration, especially 
under unfavourable temperature conditions. Hence the aldehyde group is 
not the sole reason for the reaction in the case of formaldehyde, but the 
agency which can make use of formaldehyde in the plant is specific for that 
compound. 
THE FORMALDEHYDE QUESTION. 
The question remains (see p. 424) : Is formaldehyde the first step in 
a complicated series of reactions requiring light energy in photosynthesis, 
or is it the last step in respiration, and hence converted by the plant into 
carbon dioxide? Without an answer to this primary question, the results 
with formaldehyde have no significance, as we cannot tell their real 
meaning. The obvious method of attacking this problem was to determine, 
quantitatively, the ratio between the weight lost and carbon dioxide evolved 
by the plants in respiration, with and without formaldehyde in the atmo- 
sphere. For, if formaldehyde is absorbed by the plant and converted into 
carbon dioxide, there will be more carbon dioxide evolved for a given loss 
of weight in the plant than under normal conditions. Before attempting to 
determine this, it was, however, necessary to find whether there was any 
definite relation between the weight lost and the carbon dioxide evolved 
during normal respiration, and to determine this relation if it was sufficiently 
definite. 
Quantitative Determination of the Ratio between the Loss in Weight of the 
Plants and the Carbon dioxide evolved during Respiration in Darkness. 
The only experiments in which a direct determination has been made of 
the ratio obtaining between the loss in weight of plants and the carbon dioxide 
of respiration were made some years ago by T. C. Day. 1 Day undertook an 
elaborate quantitative study of the chemical processes taking place during 
the earlier stages of the germination of barley. He found that a certain 
proportion of oxygen was absorbed and retained by the seeds, in excess of 
that oxidized to form carbon dioxide; but that, having allowed for this, 
the proportions between the loss in wet weight and dry weight of the seeds 
and the carbon dioxide evolved in respiration approximated very closely 
1 T. C. Day : Experiments on Germinating Barley and Influence of Temperature on Germinating 
Barley. Journ. Chem. Soc. Trans., 1880, pp. 645-58, and 1891, pp. 664-77. 
