at the time of the opening of its petals. As we have seen, the 

 many striking changes of color in plants after injury with the 

 resulting exposure to the atmospheric oxygen, have long been 

 subjects of investigation, but until recently such research was 

 confined to studies of the enzymes involved, to the consequent 

 neglect of the chromogens affected by these enzymes. In studying 

 the role of the oxidases, if we were to consider only the enzymes, 

 we should be neglecting the other half of the problem, for the 

 chromogens occurring in plants are the sources of all the colora- 

 tions and may very well act as oxygen carriers in the metabolism 

 of the plant. Even in 1882 Reinke^^ interested himself in the 

 substances in the plant which gave colored oxidation products 

 under the influence of oxidases and of the air. The juice of the 

 potato and of the white beet contained a chromogen which 

 became dark upon standing in the air, but it was easily changed 

 back to its original colorless state by reducing agents or by certain 

 bacteria. He thought that the colorless condition of the 

 chromogens in the living cell is due to accompanying reducing 

 substances, or else that the cell is able to oxidize the chromogens 

 through the colored state to a more highly oxidized colorless 

 condition. 



To show the distribution of these chromogens among plants 

 this outline, adapted from Chodat,^'' is given (the changes being 

 from colorless to that indicated) : 



Yellow, to green, then to blue — Boletus spp. 



Red, violet and then black — many of the higher fungi, es- 

 pecially Agaricaceae; wheat seedlings, potatoes, apples, nuts, 

 Lathyrus niger, secretions of certain ink-fish, etc. 



Brown, then black — Rhus succedana, etc. 



Violet-red — Jacohinia spp}^ 



Black — the higher fungi, especially Hygropliorus spp.; Mono- 

 tropa uniflora and Vihurnum lantana. 



« Reinke. Ein Beitrag zur Kenntniss leicht oxidirbarer Verbindungen der 

 Pflanzen-korpers. Zts. Physiol. Chem. 6: 263. 1882. 



«Chodat. Chapter on the "Oxydases" in Abderhalden's Handbuch der Bio- 

 chem. Arbeitsmethoden, III, 2d part, p. 42 ff. 1910. 



" Parkin. On a Brilliant Pigment Appearing after Injury in Species of Jacobinia 

 Report Brit. Ass'n Advancem. Sci. 1904, p. 818. 



