PART LY. | GENERAL RETROSPECT. 575 
flowers, even though they are scentless and offer no honey, or none 
that is accessible (Ranunculus, Helianthemum, Papaver, Genista), 
attract beetles in numbers. The only apparent explanation of 
these facts is that beetles are only or mainly attracted to flowers 
by bright colours. If this explanation is correct, dull-yellow must 
be an advantageous colour for plants with freely exposed honey, 
protecting them from these injurious guests. And the fact that 
dull-yellow colours only occur in flowers with exposed honey lends 
support to this view. 
Delpino goes much further in regard to the exclusion of insect- 
visitors by colour, for he supposes that dull-yellow and purple- 
spotted flowers are visited only by Diptera. But my lists show 
that almost all the dull-yellow flowers mentioned above are visited 
by Hymenoptera, sometimes in great abundance and variety. I 
have only investigated two purple-spotted flowers, namely, 
Cypripedium Calceolus, whose staminode is speckled with purple, 
and Lycopus ewropeus, whose lower lip bears reddish-purple 
spots; but both of these are visited chiefly by insects of other 
orders. 
Indirect limitation of insect-visitors by colour is instanced in 
several other cases; but such limitation is of very subsidiary im- 
portance, since it is always combined with other more powerful 
restrictions. Several bright and pretty flowers, e.g. the species of 
Dianthus, attract butterflies in great numbers; even if the 
honey was accessible to other insects their visits would be greatly 
reduced by the fact of the honey being in great part used up 
by the butterflies; but in these cases the honey is placed at 
the bottom of a tube so narrow that it is only accessible to the 
proboscis of a butterfly. 
Many light-coloured flowers, which often grow in shady places, 
are inconspicuous by day but conspicuous by night (e.g. Platan- 
thera). These are chiefly visited by crepuscular Lepidoptera, but 
insects are excluded not so much by the colour as by the 
situation of the honey at the base of long, narrow tubes. 
Limitation of insect-visits by peculiar odour is probably a more 
common phenomenon; but our present knowledge is not suffi- 
cient to admit of perfectly definite conclusions. It is obvious that 
flowers with a putrid odour are mainly fitted to attract carrion- 
flies and meat-flies, but how far their odour repels other insects 
has not yet been decided by observation. None of our native 
flowers possess odours of this kind. In like manner it is scarcely 
possible to doubt that the foul ammoniacal smell of Arum is 
