Flowers 



flowers is intensely active, and is much more vigorous 

 in the case of petals than with ordinary leaves. 



The precocious flowering of leaf-cuttings and sickly 

 trees might be due therefore simply to the increased 

 respiration which is a result of their unhappy situation 

 (see p. 332). 



There is every reason to believe, from what we know 

 of modern club-mosses, fern-spores, and moss-capsules, 

 that the original flowers were yellowish. That is also 

 very probable from the ordinary development of the 

 green chlorophyll of leaves.^ The colourless plastids 

 first become yellow (Xanthophyll) and then turn green. 



In a developing petal, the great demand for food 

 material of the stamens and carpels might well prevent 

 the formation of the green colour. Then one of two 

 different things may have happened. 



The process of economising might have been con- 

 tinued by suppressing the formation of the yellow, leav- 

 ing the petals pure white. Or the yellow may have been 

 changed into red, similar to that of some fading autumn 

 leaves, and which is due to chrysophyll or carotin. 



Other colouring matters seem to have then appeared, 

 probably developed independently through the action 

 of enzymes or in some as yet unexplained way. 



The proportion of the various colours has been 

 calculated by Kerekgyarto,^ who found the percentages 

 to be as follows : — 



Unless, however, one could investigate all the 170,000 

 kinds of flowers known, one would not have the data 

 from whichto draw conclusions. 



Ill 



