Botany: The Science of Plant Life

by Norman Taylor

While color of flowers seems as though it were attraction enough, it is very likely that their fragrance or perfume is still more seductive in its power of luring insect visitors and repelling useless ones. Poets have called this perfume the soul of the flower, and in its almost intangible beauty it might well be so called were it not for the fact that it appears to be of not the slightest use, except as a lure. In all the equipment of seduction there is none like this fragrance of flowers for attracting insects.

Flowers, then, have things to offer to insects which the latter need. Nectar and pollen are the chief, and where these merely bread and butter objects are not enough, or sometimes in addition to them, the flower is dressed out in gorgeous colors or perfumed with a fragrance beyond the dreams of the fairest bride. What insects do to complete the fertilization of such a legion of beauties makes up the romance of the flowers. Perhaps not even in man himself is this creation of new life so surrounded with beautiful ideas. Also, as in man, it sometimes is bound up with an almost fiendish cruelty and cunning. Some of these visitors and what they do, but unfortunately only a very few, can be mentioned here. They must serve as types or examples of what is going on all about us on any summer day.

The common blue columbine, much grown in gardens for its beautiful blossoms, always has the flowers hanging upside down, a habit that admirably serves to keep its pollen from rain. The opening and closing of many flowers in cloudy weather, or at night, may be for the same reason. Everyone knows the five blue spurs into which the petals of columbine are produced. At the very end of each spur, which is always curved, the flower secretes a considerable quantity of honey. This, one of the greatest attractions to bees, leads inevitably to a visit from one. The bee, in order to reach the honey, hangs on to the inverted flowers, clutching the base of the spur with its foreleg, and further securing itself by the mid or hind legs, which grasp the slender column into which, in the columbine, the stamens and pistils are crowded. In its anxiety to reach the honey the bee pokes its head as far into the spur as possible, but it gets in only a fraction of the full length of the tube. To reach the honey it extends its sucking apparatus, which is a complicated mechanism for this purpose on the head of nearly all insects, and which will hereafter be called by its true name of proboscis. It happens that bees can easily bend the proboscis downward or toward their own body, but only with considerable difficulty can they bend it in the opposite way. And yet the honey in the curved tip of the columbine can only be reached by curving the proboscis to fit the tube, and in this process the bee’s body for nearly half its length is forced to touch the anthers. While these are close to the stigma, they produce pollen only on their outside surface, where it is, of course, scarcely likely to reach the stigma, but must be brushed off by the contortions of the bee’s body in reaching the honey. The hairy body of the bee, coated with pollen, goes next to perhaps an older flower of the columbine. Heedless of any change in the flower the bee goes straight for the honey in one of the spurs, again catches hold of the only available support in the center of the flower. But this time, instead of brushing pollen off the exposed anthers, it brushes it off its own body to the stigmas, which, at a slightly later stage than in the one just described, are branched and perfectly adapted for collecting the pollen with which the bepowdered bee can hardly avoid dusting them. Cross-fertilization is of course assured, but it seems a precarious business at best, as the number of bees with a proboscis long enough to do the work is limited. The columbine, by a kind of uncanny foresight, is so constructed that bees or other insects that try to reach the honey and are not provided with a sufficiently long proboscis, nevertheless in further attempts upon other flowers, inevitably cross-fertilize them without reaping their reward. One or two kinds of bees, as though in retaliation for this subterfuge of the columbine, make short work of the honey by biting a hole in the spur and forthwith sucking out the honey without so much as touching anther, pollen, or stigma. The reply of the columbine to this ravaging of its chief attraction is that finally, as a last resort, and by a new movement of its reproductive organs, it is self-fertilized. Here the shape of the flower, the original position of the pistil and anthers, the exposure of pollen only in such a direction that, while a chance of cross-fertilization still exists, it can hardly ever fertilize its own stigmas, all point to cross-fertilization as the plant’s greatest requirement. And yet failing this, it falls back on self-fertilization rather than endure barren sterility.

While the columbine by its spurs and other interior structure succeeds nearly always in holding a bee long enough to insure its being dusted with pollen, the common barberry bush of Europe ([Figure 70]), also much planted in American gardens for ornament, actually drives bees away by sharp blows of its stamens, so that self-fertilization shall not result from the visit. In this shrub the petals partly cover the stamens unless the latter are disturbed, and, in fact, the curved tip of the petals forms a kind of socket into which each of the six stamens are fitted. The position of these is such that any insect