No one can doubt who watches a meadow on a summer's day that insects are attracted by the scent and the colours of the flowers. The whole field is busy with their jubilant hum. These little creatures have the same sense of beauty that we have. What room there is for thought in that fact! There is a subtle bond of mental union between ourselves and the creatures whom we so often despise. There is a joy widespread and multiplied beyond our highest calculation. What a deadly blow to that egotism of man which thinks of all beauty as made for him alone!
But I return to the argument. We have presented to our notice three kinds of attraction which operate upon insects—the conspicuousness of colour and form, the beauty of the smell, and the pleasant taste of the honey. No one, as I have said, who watches a meadow or a garden on a summer's day can for a moment doubt the operation of these causes, or question the direct action of insects in producing the fertilization of flowers. In that sense the beauty of a flower is clearly of direct use to the flower which exhibits it. It is better for it that it should be fertilized by insects than not fertilized at all; but is it better for it to be fertilized by insects than by the wind, or by some other agency, if such exist?
This shall be the subject of inquiry. But before we can answer it, we must go a little afield and collect some other of the facts of the case.
The conclusion that beauty is useful for the fertilization of the flower does not rest merely on the general phenomena of a summer meadow. It is confirmed by many other observations. Flowers are not merely attractive in themselves; they are frequently rendered attractive by their grouping. Sometimes flowers individually small are gathered into heads, or spikes, or bunches, or umbels, and so produce a more conspicuous effect than would result from a more equal distribution of the flowers; sometimes yet more minute flowers or florets are gathered together into what appears a single flower, and often have the outer florets so modified both in shape and colour as to produce the general effect of one very brilliant blossom, as in the daisy or the marigold.
Sometimes the same result is produced by "the massing of small flowers into dense cushions of bright colour."[4] This, as is well known, is of common occurrence with Alpine flowers; and this mode of growth, as well as the great size of many Alpine blossoms as compared with that of the whole plant, and the great brilliance of Alpine plants as compared with their congeners of the lowlands, have all been explained by reference to the comparative rarity of insects in the Alpine heights, and the consequent necessity, if the plants are to survive, that they should offer strong attractions to their needful friends.[5] A similar explanation has been offered for the brilliant colours of Arctic flowers.[6]
Furthermore, this curious fact exists, that of flowering plants a large number do not ripen or put forward their pistils and stamens at the same periods of their growth: in some cases the pistil is ready to receive the pollen whilst the anthers are immature and not ready to supply it: such are called proterogynous. In other cases the anthers are ripe before the pistil is ready to receive the pollen: these are proterandrous. In either case the same event happens—that the ovules can never be fertilized by the pollen of the same blossom, nor without some foreign agency, generally that of insects.
Lastly, there is a large number of plants, including a great proportion of those with unsymmetrical blossoms, of which the flowers have been shown to be specially adapted by various mechanical contrivances for insect agency. Nothing, as is well known, is more marvellous than the variety and subtlety of the arrangements for the purpose which exist in orchidaceous plants, as explained by the patience and genius of Mr. Darwin.
In view of these facts it would be impossible to deny that conspicuousness is one of the agencies in force for the fertilization of flowers; that, to use the recent language of Mr. Darwin, "flowers are not only delightful for their beauty and fragrance, but display most wonderful adaptations for various purposes."[7]
So far we have considered the evidence which is affirmative, and in favour of the explanation of the existence of beauty in flowers; we have found clearly that beauty, or rather conspicuousness, is in many cases useful to the plant. But beauty is by no means the only agency in this necessary process. On the contrary, the agencies actually in operation are very numerous.