52 
Colour in Flowers. 
the study of floral natural history, clearly recognised this. “ The 
corolla of these flowers,” he says, “ is either wholly inexplicable, or 
else it serves to enable the flowers to strike the eyes of the bees 
which collect their pollen, at a distance.” Darwin, who more than 
half a century later took up and extended Sprengel’s work, inter¬ 
preting the extraordinary adaptations of floral structure in the 
light of his theory of natural selection, takes essentially the same 
view. “ We can understand ” he writes in “ The Effects of Cross 
and Self-Fertilisation,” “the considerable size and striking colours 
(of flowers), and in certain cases also the bright colouration of 
neighbouring parts, as for instance, flower-stalks and bracts. By 
these means are they made conspicuous to insects, according to the 
same principle that in those fruits which are eaten by birds there is 
a sharp contrast with the green leaves, so that the former may be 
seen and thus seeds freely distributed.” In some flowers the con¬ 
spicuousness is obtained even at the cost of the reproductive 
organs, as for instance in the ray-florets of many Compositae, in 
the outer flowers of Hydrangea and the terminal flowers of the 
Feather-hyacinth or Muscari. There is also ground for the belief— 
and this was Sprengel’s opinion—that flowers differ from one 
another in colour, in correspondence with the species of insects 
which visit them. Hermann Muller, who for many years devoted 
the whole of his leisure to the study of flowers and insects, and 
undoubtedly did more than any other naturalist to systematise the 
whole subject, took it for granted that the colour of flowers serves 
to attract insects, and made experiments to ascertain if given 
species of bees were specially attracted by given colours. Lubbock 
made similar experiments, and both concluded that bees have 
special colour-preferences. Upon these results, taken together with 
an enormous series of observations on the relative numbers of 
different species of insects actually visiting flowers of different 
colours, Muller founded a theory of the evolution of floral colour as 
part of his general theory of the evolution of entomophilous flowers. 
Grant Allen, too, published a work on the Colours of Flowers, the 
conclusions of which do not differ essentially from Muller’s. 
It was therefore with some surprise and incredulity that those 
who follow the progress of floral natural history received the conclu¬ 
sions of Professor Plateau of Ghent, published in several papers 
from 1895 to 1902. As the result of elaborate experiments, 
Professor Plateau denies that there is proof of the perception of 
the colours of flowers by insects, and holds that it is the scent alone 
