36 Supposed Katracellular Photosynthesis of Carbon Dioarde, ete. 
Usher and Priestley have, therefore, not founded the formaldehyde 
hypothesis upon any surer basis than had been already established for it by 
Pollacci* and by Curtius and Reinke,t the only established facts being that 
chlorophyll decomposes when exposed to light in the presence of oxygen and 
in the presence or absence of carbon dioxide, and that one of the products of 
its decomposition is formaldehyde. This production of formaldehyde does 
not, however, necessarily represent the primary stage in photosynthesis, but 
is either one of the later ones or a more or less accidental phenomenon 
shown either in abnormal or dead chlorophyllous cells and tissues or by 
extracted chlorophyll. In any case we have as yet no satisfactory proof 
that the production of formaldehyde in dead cells or extracted chlorophyll 
when exposed to light is accompanied either by a decomposition of carbon 
dioxide or by a production of oxygen or hydroxyl. 
* © Atti d. Instit. Bot. Pavia,’ 1900, p. 45; 1902, p. 8; and 1904. 
+ ‘ Ber. d. Bot. Ges.,’ 1897, vol. 15, p. 201. 
