490 THE AMERICAN NATURALIST [Vol. LVI 



pigments took place we have no means of determining, 

 but it may have been before even the flagellum itself had 

 begun. This advance and the subsequent concentration 

 of the pigments into definite chromatophores or chloro- 

 plasts doubtless immensely increased the efficiency of the 

 organism in producing the food which was necessary to 

 it. The recent work of Baly and his collaborators be- 

 comes here again of the first importance, and though the 

 subject of the part played by chlorophyll in photosyn- 

 thesis belongs rather to botany and chemistry than to 

 zoology, I may perhaps for the sake of completeness be 

 allowed to refer to it very briefly. I have already said 

 that Baly brought about the synthesis of formaldehyde 

 from COo and H2O under the influence of rays of very 

 short wave-length (A = 200iu,/t) from a mercury-vapor 

 lamp. He was also able to show that when certain col- 

 ored substances were added to the solution of carbon 

 dioxide in water the same reaction took place under the 

 influence of ordinary visible light. His explanation of 

 this process is that the colored substance known as the 

 photocatalyst absorbs the light rays and then itself radi- 

 ates, at a lower infra-red frequency corresponding to its 

 own molecular frequency, the energy it has absorbed. At 

 this lower frequency the energy thus radiated is able to 

 activate the carbonic acid, so that the reaction leading 

 to the formation of formaldehyde can and does take 

 place. In the living plant this synthesized formaldehyde 

 probably at once polymerizes to form sugars. 



Malachite green and methyl orange, as well as other 

 organic compounds, were found to act as photocatalysts 

 capable of synthesizing formaldehyde, and Moore and 

 Webster's work had previously shown that inorganic 

 substances, such as colloidal uranium oxide and colloidal 

 ferric oxide, can do the same. Chlorophyll in living 

 plants may with some confidence be assumed to operate 

 in a similar way, though no doubt the series of events is 

 more complex, since the green pigment itself is not a 

 single pigment, and others, such as carotin and xantho- 

 phyll, are also concerned. 



