IN FRESH- WATER ALG.^ 109 



down. The result demonstrates that supplied in this manner the 

 vapours of these simple organic substances can substitute carbon 

 dioxide quite well, there being 3-8 rngrms. of nitrogen with the 

 formaldehyde vapour and 7-4 rngrms. with the methylic alcohol, 

 as against 0-7 mgrm. in the control. This does not show quantita- 

 tively that methylic alcohol is better as a nutrient than formal- 

 dehyde, for with somewhat increased concentrations both vapours 

 would kill the growing green cells, and it is a difficult problem so to 

 regulate the concentration of each at these excessive dilutions that 

 the maximum beneficial result is obtained. The real point is that 

 these vapours of simple organic substances, when sufficiently dilute, 

 act not as poisons to the green cell but as nutrients which can replace 

 carbon dioxide. 



The bearing of these results upon the fundamental hypothesis 

 of Baeyer, that the first step in the synthesis in green cells of the 

 organic from the inorganic is formaldehyde, is so intimate that a 

 little more consideration appears desirable. Hitherto this hypo- 

 thesis has rested mainly upon circumstantial evidence. No one 

 has ever been able to demonstrate the presence of formaldehyde in 

 the living cell. Various solutions of chlorophyll and emulsions of 

 chlorophyll in water, or upon colloidal membranes, such as gelatine, 

 have been exposed to light, and afterwards formaldehyde has been 

 tested for by delicate chemical tests. The results have been con- 

 tradictory; some observers have found formaldehyde and others 

 have failed, to detect it. But we have previously shown that 

 practically any organic system, when exposed to light, yields formal- 

 dehyde. Hence the presence of formaldehyde under such conditions 

 means nothing and probably comes from a reversed system, not of 

 building up but of breaking down of organic substances. Even if 

 formaldehyde could be shown intra vitally in a living cell it might 

 only mean excessive light exposure and breaking down of living 

 substance and not building up. Attention may again be drawn 

 to the fact that the lethal action of light upon bacteria and other 

 living cells is probably due to such a reversed reaction, in which 

 formaldehyde and other simple and poisonous organic substances 

 are set free. 



The other channel of approach experimentally to this question 

 is more promising namely, Can these simple organic substances act 

 as nutrients for cells ? If formaldehyde be the primary stage in 

 photo-synthesis by which green cells are nourished, then it ought 



