This section is from the book "On British Wild Flowers Considered In Relation To Insects", by John Lubbock. Also available from Amazon: Nature Series On British Wild Flowers Considered In Relation To Insects.
The flowers of our gardens differ much in size and colour from those of the same species growing wild in their native woods and fields: this is due partly to cultivation, but still more to the careful selection of seeds or cuttings from those plants, the flowers of which show any superiority over the others in size or colour.
Even amongst wild flowers, however, recent researches have proved that the forms and colours have been modified in a similar manner: the observations of botanists, especially of Sprengel and Darwin, have shown that the forms and colours of wild flowers are mainly owing to the unconscious selection exercised by insects, although no doubt the existence of a certain amount of colouring matter is, as we see in the autumn tints, in various fungi, seaweeds, etc, due to other causes.
Sprengel appears to have been the first who perceived the intimate relations which exist between plants and insects; and Geranium sylvaticum (see p. 1) will always have an interest as being the flower which first led him to his researches. In the year 1787 he observed that in the corolla of this species there are a number of delicate hairs; and, convinced, as he says, that "the wise Author of Nature would not have created even a hair in vain," he endeavoured to ascertain the use of these hairs, and satisfied himself that they served to protect the honey from rain.
His attention having thus been drawn to the subject, he examined numerous other flowers with great care, and was surprised to find how many points in reference to them could be explained by their relations to insects.
The visits of insects are of great importance to plants in transferring the pollen from the stamens to the pistil. In many plants the stamens and pistil are situated in separate flowers: and even in those cases where they are contained in the same flower, self-fertilisation is often rendered difficult, or impossible; sometimes by the relative position of the stamens and pistil, sometimes by their not coming to maturity at the same time. Under these circumstances the transference of the pollen from the stamens to the pistil is effected in various ways. In some species the pollen is carried by the action of the wind; in some few cases, by birds; but in the majority, this important object is secured by the visits of insects, and the whole organisation of such flowers is adapted to this purpose.
To the honey are due the visits of insects; the sweet scent and bright colours of the flowers attract them; the lines and circles on the corolla guide them to the right spot; and, as we shall see, there are a number of curious contrivances all tending to the same object. But while Sprengel's deep religious feeling thus gave him the clue which has thrown so much light on the origin and structure of flowers, the comparatively low conception of creative power which was in his time, and, indeed, until recently, prevalent, led him to assume that each flower was created as we now see it, and prevented him from perceiving the real significance of the facts which he had discovered; while the true explanation could scarcely have escaped him if he had possessed that higher view of creation which we owe to Mr. Darwin. Though he observed that in many species the stamens and pistil are not mature simultaneously, and that such plants therefore cannot fertilise themselves, but are generally dependent on the visits of insects, he appears to have considered that these visits were arranged mainly in order to overcome the difficulty of fertilisation thus resulting; and hence, perhaps, the oblivion into which his work, though so interesting and suggestive in itself, so full of curious and careful observations, was allowed to fall. For there is an obvious inconsistency in the coexistence of two elaborate sets of arrangements, one tending to preclude, the other to effect, self-fertilisation; in supposing that in the first place the stamens and pistil were so arranged that the pollen of the one might not fertilise the other; and, secondly, that elaborate contrivances were devised to promote the visits of insects, and compel them to transfer the pollen from the stamens to the pistil: a result which might have been obtained so much more simply by a slight alteration of the flower itself.
It is the more remarkable that this did not strike Sprengel, because he expressly observes in one passage that, "Die Natur nicht will dass irgend einer Zvvitterblume durch ihren eigenen Staub befrlichtet werden solle" (Nature does not choose that any complete flower should be fertilised by its own pollen). Yet though thus so near the truth, he failed to perceive the true importance of the visits of insects. Subsequent observers, though in some cases recognising the advantage of fertilising one flower by pollen from another, did not connect these observations with Sprengel's discoveries; and our illustrious countryman Mr. Darwin was the first to bring into prominence the fact that the importance of insects to flowers consisted in their transferring the pollen - not merely from the stamens to the pistil, but from the stamens of one plant to the pistil of another.
While then from time immemorial we have known that flowers are of great importance to insects, it is only comparatively of late that we have realised how important, indeed how necessary, insects are to flowers. For it is not too much to say, that if, on the one hand, flowers are in many cases necessary to the existence of insects; insects, on the other hand, are still more indispensable to the very existence of flowers: - that, if insects have been in many cases modified and adapted with a view to obtain honey and pollen from flowers, flowers in their turn owe their scent and colour, their honey, and even their distinctive forms to the action of insects. There has thus been an interaction of insects upon flowers, and of flowers upon insects, resulting in the gradual modification of both.