FLOWER PIGMENTS. 83 



That is, in sunlight the}" absorb carbon dioxide and exhale 

 oxygen ; while at night or during great activity the}^ live like 

 animals, using up the oxygen from the air and producing 

 carbon dioxide. These processes are alwaj^s going on more 

 or less simultaneoush'. During the time of flowering we 

 know that the animal side of the plant is verj' active, as a 

 considerable production of heat, which can onlj- result from 

 oxidation, is then found to occur in the flowers. This means 

 that the flowers at this time are the seat of active production 

 of carbon dioxide. But since this compound is acid in reac- 

 tion, it follows that the pigments in the flower petals will take 

 on that color which corresponds to the acid reaction ; that is, 

 the flowers will assume the ordinar}' color as met with, depend- 

 ing upon what pigments are present. In the earlier life of 

 the flower, however, when it is simply living with the vege- 

 table side of life predominant, there is not an acid reaction 

 due to the presence of carbon dioxide and the petals are 

 green, as we find them in 3'oung flowers. If the more or less 

 greenish petals of an immature red flower, for example, be 

 placed in water slightly acidified, they will assume the red 

 color of the mature flower. This shows that the pigment is 

 already present, but that the reaction is not acid. There are 

 probably other substances of acid reaction also produced in 

 the maturing flower, but the mention of carbon dioxide will 

 be enough to indicate the trend of thought. 



The theory of the physiology of the pigments to which 

 our speculations lead may be briefly summarized as follows : 

 In the petals of the young flower there exist certain of the 

 three primary pigments in certain proportions. The reac- 

 tion is alkaline, however, or at least not acid, and no matter 

 what pigments are present the color is green. But later, as the 

 animal life of the flower becomes more pronounced and the 

 bud matures, the carbon dioxide and other acid substances 

 thus produced change the reaction of the juices of the petal 

 to acid, and the red, yellow or blue color of the pigment or pig- 

 ments develops and the flower gradually assumes its final hue. 



