THE CHLOEOPHYLL APPARATUS 



165 



placed in sunlight, bubbles of oxygen will be given off by 

 the leaves and will rise into the burette. If no carbon 

 dioxide is in the water, no oxygen will be given off. 



There is nothing certainly known at present as to the 

 details of the changes which connect these two phenomena. 

 It has been suggested by Baeyer that the carbon dioxide is 

 decomposed with the formation of carbon monoxide and 

 oxygen, according to the equation 2C0 2 = 2CO + 2 . At 

 the same time there is a decomposition of water, possibly 

 in the way denoted by the equation 2H 2 = 2H 2 + 2 . 

 The oxygen is given off, the volume being found, when care- 

 fully measured, to be equal 

 to the volume of carbon 

 dioxide undergoing de- 

 composition* The carbon 

 monoxide and the hydro- 

 gen are then thought to 

 unite, producing formal- 

 dehyde, a body repre- 

 sented by the formula 

 CH 2 0, or preferably 

 HCOH. This suggested 

 series of reactions agrees 

 fairly closely with the ob- 

 served facts, but it must 

 not be regarded as anything more than an hypothesis. Indeed 

 there are considerable difficulties in accepting it as it 

 stands. There is no evidence that carbon monoxide is 

 formed. Experiments have shown that this gas is quite 

 useless to a plant ; if it is supplied in the place of the 

 dioxide, the formation of carbohydrates does not take 

 place. Nor has 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. If administered directly to a 



FIG. 90. APPARATUS TO SHOW THE EVOLU- 

 TION OF OXYGEN BY A GREEN PLANT IN 



SUNLIGHT. 



