THE COLOURS OF FLOWERS 
IOI 
found in the genus to which the species belongs. E.g. in Dianthus, 
some species show red, some white, some yellowish or purple-violet 
corollas, but none blue. Now in the cultivated pinks and carnations 
( D . Caryophyllus ) red, white, yellowish, and violet colours are known 
in every shade, mixture and variegation, but no efforts of horticul- 
turists can produce a blue carnation. Other examples are found in the 
stock (Matthiola), wall-flower (Cheiranthus), aster (Callistephus) and 
most other cultivated flowers. Sometimes the range of colour in the 
species is that defined by the order rather than by the genus. A great 
many flowers do not normally vary in colour at all, and horticulturists 
sometimes find considerable difficulty in starting the variation necessary 
before new races can be obtained. The most common method is change 
of soil, manure, light, heat, &c. All these conditions have in nature certain 
influences on the colour of flowers (no definite rules can be framed, as 
two flowers of the same colour but of different species are often affected 
in opposite ways by the same agent), and when all are changed together, 
the plant seems as if it received some kind of a shock which may cause 
variation. Once variation in a hitherto fixed colour can be started it 
often continues for a long time, keeping, however, within certain 
limits, as we have explained. It is to be noted that, with the excep- 
tion of the long cultivated hyacinth, blue flowers do not vary to 
yellow, even if there be yellow species in the genus. Red varies 
towards yellow rather than towards blue. All colours vary readily to 
white. 
As regards the question of the meaning and function of 
colour in flowers there can be no doubt that it is largely 
bound up with pollination by insects. If however we set out 
only from the higher plants, we shall as usual come across 
cases that cannot be explained in the light of the information 
there obtained. The spores of Cryptogams are generally 
coloured, yellow or brown, less often red or green. What 
the meaning of this fact is, we do not know. Colours are 
well known to appear in many chemical reactions and it is 
quite likely that many colours are of this accidental kind 
without any particular significance in the life-history. Or it 
may be that the colour of spores protects them from the 
action of light (which is very fatal, for example, to the spores 
of bacteria). However this may be, yellow is prevalent in 
spores and pollen grains, and the conspicuous colour of 
many anemophilous flowers, e.g. Abies and other Conifers, 
Corylus, &c., some Grasses, and so on, is no longer a sur- 
prising exception, as it is if colours are regarded as only 
concerned with insect visits. If the corolla was derived from 
stamens, it would seem possible that its colour was yellow at 
first and that all the other colours are subsequent derivatives. 
