The singularly inconspicuous flowers
of the Fly Ophrys (O. muscifera), as I have elsewhere shown, are rarely
visited by insects; and it is a strange instance of imperfection, in
contradiction to the above rule, that these flowers are not
self-fertile, so that a large proportion of them do not produce seeds.
The converse of the rule that plants bearing small and inconspicuous
flowers are self-fertile, namely, that plants with large and conspicuous
flowers are self-sterile, is far from true, as may be seen in our second
list of spontaneously self-fertile species; for this list includes such
species as Ipomoea purpurea, Adonis aestivalis, Verbascum thapsus, Pisum
sativum, Lathyrus odoratus, some species of Papaver and of Nymphaea, and
others.
The rarity of the visits of insects to small flowers, does not depend
altogether on their inconspicuousness, but likewise on the absence of
some sufficient attraction; for the flowers of Trifolium arvense are
extremely small, yet are incessantly visited by hive and humble-bees, as
are the small and dingy flowers of the asparagus. The flowers of Linaria
cymbalaria are small and not very conspicuous, yet at the proper time
they are freely visited by hive-bees. I may add that, according to Mr.
Bennett, there is another and quite distinct class of plants which
cannot be much frequented by insects, as they flower either exclusively
or often during the winter, and these seem adapted for
self-fertilisation, as they shed their pollen before the flowers expand.
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