124 BOTANICAL GAZETTE [FEBRUARY 
increases, one would naturally seek the cause of this, and is led to 
investigate the relationships which may exist between the various 
plant pigments. 
Ewart (16, 17) believes that carotin after photo-oxidation or 
partial disintegration forms. a massive hydrocarbon combination 
(the phytol radicle of chlorophyll) whose addition is necessary to 
convert the dicarboxylic glaucophyllin into the tricarboxylic 
chlorophyll. Perhaps this might explain the disappearance of 
carotin as chlorophyll forms. The bridge between the two yellow 
pigments is not so difficult to cross, for one of them (xanthophyll) 
is simply the oxidation product of the other (carotin). 
Some believe that chlorophyll may act as a sensitizer, and others 
that it may act as a photic or lytase enzyme which converts carbon 
dioxide and water into carbohydrates. Ewart (16) has shown 
that chlorophyll may act as an enzyme according to the following 
three equations: 
(1) 2 C3, H.N,Mg(COOH) (COOCH;) (COOC,,H,») +36CO.+ 
16H,0=2 CyH 60.+440.+2Cs1H3NsiMg(COOH): Amorphous 
chlorophyll+carbon dioxide and water would form xanthophyll 
or carotin, oxygen, and glaucophyllin. (2) C,H ss0,+24H,O+ 
70,.=2 C.H,O0H+3C6H,.06+3CsH,.06+4 HCHO. Carotin or 
xanthophyll+water+oxygen equals phytol+levulose+glucose+ 
formaldehyde. (3) 2C.H;,OH+2C,,H,N,Mg (COOH).+4CO,= 
2C;;H..N,Mg (COOH) (COOCH;) (COOC..H,.)+30,. Phytol+ 
glaucophyllin and carbon dioxide form amorphous chlorophyll 
and oxygen. 
Reaction 2 takes place in the light with the aid of an oxidase 
enzyme. : 
Since many chemical reactions are reversible, and since phytol 
splits off the chlorophyll molecule easily, it is possible that the 
sugars and phytol may react to form carotin or xanthophyll, which 
would account for the greater accumulation of yellow pigments in 
autumn leaves and also for the disappearance of the chlorophyll. 
Film experiments carried out by Ewart (17) showed that carbon 
dioxide combines with chlorophyll to form xanthophyll and a 
colorless waxy substance. The combination takes place in the 
presence of water and is accelerated by sunlight. It is thus seen 
