8 
or 
as soon as any flower exhibits any tendency to variation in the 
direction of brilliancy of colour, it is probably visited by these 
insects, and its propagation thus ensured, the tendency to brilliancy 
of colour being increased by the law of heredity, and further 
confirmed by suitable conditions of growth; and it is true that, 
toa certain extent, this may take place with regard to dark-coloured 
flowers (by reason, perhaps, of their sweeter scent); but owing 
possibly to colour being generally more attractive to insects, and 
other causes, these latter seem to fail in the competition with their 
more fayoured rivals. It is interesting to consider the rationale of 
this transportation of a germ from a plant of more or less brilliant 
colour to another, by the ultimate effects of which the stock is as 
it were established. Now it is probable that flowers owe their 
colour to the fact of the existence of a very delicate tissue, which 
has the property of absorbing some rays, and rejecting others (for 
all flowers are naturally colourless before exposure to light), but in 
some cases, owing perhaps to various causes, this tissue absorbs 
rays of light of a different hue from those which we are accustomed to 
consider as belonging to the flower in question, and the result is 
a variation in colour. As soon, then, as this variation (however 
slight it be) appears, it is taken advantage of by butterflies, which, 
attracted perhaps by the difference in hue, visit the flower and 
transmit the germs to another flower in which, in course of time, 
the variation in colour becomes fixed, partly by the transmission of 
the germ having taken place at the proper time and under fayour- 
able conditions, and partly also from the action of the law of 
heredity by which any variation in a plant is, under favourable 
circumstances, liable, not only to be again produced, but absolutely 
increased in amount with each case of reproduction, so that the 
variation is now developed in an ever-increasing ratio until it 
becomes more or less confirmed. In connection with this subject, 
the question suggests itself{—do cultivated plants come under the 
same law as domesticated in contradistinction to wild animals ? 
We kaow that the former, at least sometimes, are not so fertile as 
the latter, so that it would seem that, by confinement or domestica- 
tion, a certain degree of change is produced in the generative 
organs inducing partial sterility. Now, there seems reason to 
believe that in proportion as a plant tends to vary, so does it suffer 
in its fertility. It is the domestication or cultivation of plants 
which often produces variation, and this probably means with 
cultivated plants an increase in brilliancy of colour of the flowers, 
which would seem, probably by inference, to be attended (at least to 
some extent) by infertility. The same suggestion may, I think, also 
be applied to wild flowers, the brilliant colour of which we have 
seen to be often caused by variation ; but the tendency thus pro- 
duced to decrease in fertility may be here, perhaps, in some measure 
counteracted by the continual intermixture or crossing of different 
