THE CHLOKOPHYLL APPAKATUS 157 



any formation or liberation of hydrogen ever been detected so 

 long as the plant is maintained in normal conditions. 



The formation of formaldehyde, again, is very difficult 

 of proof. It very readily undergoes change, and therefore 

 is difficult to detect in a plant. It has been found, how- 

 ever, that if Spirogyra is fed with a compound of form- 

 aldehyde and sodium-hydrogen-sulphite, which slowly 

 evolves the former in the presence ot water, a formation 

 of carbohydrates occurs. This cannot, however, be accepted 

 as proof that formaldehyde normally subserves this purpose. 



There is, however, a certain amount of evidence that 

 formaldehyde plays some part in photosynthesis. Bouilhac 

 and Treboux have succeeded in getting plants to grow in 

 a very dilute solution of it. Moreover, formaldehyde has 

 been obtained from plants by distilling leaves which have 

 been exposed for a long time to light and subsequently 

 soaked in water. Even in these experiments, however, it 

 is not certain how it was produced. In any except very 

 dilute solutions it is intensely poisonous to plants. 



Within the last few years formaldehyde has been detected 

 in leaves which have been plucked after exposure for some 

 hours to a bright sun. The test was devised by Mulliken, 

 Brown, and French, and is extremely delicate. To apply it 

 take 1 c.c. of a 5 per cent, solution of gallic acid in absolute 

 alcohol, add about 3 c.c. of pure concentrated sulphuric 

 acid so that the two fluids do not mix, and allow a small 

 quantity of the suspected extract of the leaves to stream 

 down the side of the test tube in which the experiment is 

 being conducted. The presence of formaldehyde will be 

 indicated by the formation of a blue-green ring at the zone 

 of contact of the upper and lower liquids. 



If we concede that formaldehyde is very probably the 

 first stage in the photosynthetic process, a consideration of 

 the probable decomposition seems to lead us to the view 

 that the carbon dioxide and the water are made to interact 

 without the liberation of carbon monoxide, and that the 

 reaction may be represented by the equation C0 3 + H 3 = 



