356 



Messrs. I. Jorgensen and F. Kidd. 



This conclusion is in strong contrast to that drawn by Willstatter from his 

 own experiments (14, 15). "In spite of numerous experiments with 

 extracted chlorophyll or isolated chloroplasts we have been unable to 

 reproduce the phenomena of carbon assimilation outside the plant." 

 Unfortunately this important statement was not accompanied by any 

 experimental evidence. It is, however, the view to which the present 

 authors have been led. 



We do not intend to deal with the indirect evidence brought forward by 

 Usher and Priestley in support of their theory, such as the production of 

 formaldehyde from carbon dioxide and water exposed to light in quartz 

 tubes ; these and similar experiments by other investigators have been 

 criticised adversely by H. A. Spoehr (8). 



With regard to the direct evidence of the production of formaldehyde in 

 chlorophyll-containing systems, we have not been able to obtain any evidence 

 of formaldehyde production in systems containing chlorophyll, carbon 

 dioxide, and water. Formaldehyde production was always limited to systems 

 containing oxygen. But even minute traces of oxygen are capable of 

 accounting for small quantities of formaldehyde. If crude chlorophyll is 

 used the small amount of oxygen present in the commercial nitrogen and 

 carbon dioxide obtained from gas cylinders can give rise to a large 

 formaldehyde production. 



Although some of Usher and Priestley's results can be explained by the 

 oxidation of crude chlorophyll, other of the results can hardly be interpreted 

 as due to this cause. Thus these authors give an account of some experiments 

 (1911, p. 103), of which they state that they carried out a considerable 

 number with concordant results. In these experiments there were exposed 

 to light two pairs of sealed glass tubes containing : 



(1) Chlorophyll, air, catalase, and caustic potash, (2) chlorophyll, air, and 

 caustic potash ; (3) chlorophyll, air, catalase, and caustic potash, (4) chloro- 

 phyll, catalase, air, and carbon dioxide. 



They found that the chlorophyll bleached much more quickly in tubes 2 

 and 4 than that in 1 and 3. While 3 gave only a trace of formaldehyde,- 

 4 exposed to light for the same time gave a marked formaldehyde reaction. 



It is indeed tempting, and seems at first sight quite reasonable, to assume 

 that the increased quantity of formaldehyde produced in 4 as compared with 

 3 is due to the carbon dioxide, and that 1 remains green longer than 2 

 because in the former the catalase destroys the hydrogen peroxide responsible- 

 for the bleaching. 



But considered more closely these experiments become quite concordant 

 with our results. Usher and Priestley have neglected the possibility of the- 



