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 :— 
Green. | Yellow. | White | Red. | Blue. | Lilac. 
Monocotyledons (207 species) | 2.12 | 29.82 | 32.23 | 18.23 | 8.99 | 4.73 
Dicotyledons (1795 species) .| 6.28 | 12.07 | 16.9 | 25.12 | 3.91 | 4.90 
Unless, however, one could investigate all the 170, 000 
kinds of flowers known, one would not have the data 
from whichto draw conclusions, 
111 
