nation, can set no seed. For many trees, and for grasses generally, the office of transporting the pollen is performed by the wind. And, "as the wind bloweth where it listeth," it may waste a million pollengrains for every one it lodges on a stigma. Hence the prodigality of pollen. If you walk through a field of corn, you will note how generously the tassel yields its pollen to the wind. If, toward the last of May, you shake a branch of pine, you will see floating from it a cloud of pollen-grains.
Having seen the largest prodigality, we will search now for the closest economy.
In many of the violets we find, in addition to the showy flowers, another set borne on runners and concealed under leaves. In the fringed polygala we have another case of dimorphism. In one flower the petals are of richest pink, two of them spreading out like wings, and the other, keel-shaped, crested and fringed. Another flower, which never opens, is borne close to the ground, or even in the ground, on subterranean shoots. Now, these ground flowers of the violet and polygala are self-fertilizing. One grain of pollen is enough for one seed, and that is all which Nature, in these flowers, will furnish.
You will observe now that the pine and the corn, in general all conifers and grasses depending for fertilization on the wind, have colorless flowers and much pollen, and that concealed flowers are without color and have but little pollen. We begin to suspect that color stands in some relation to the needs of the flower. In the grasses and pines it would be of no use, as the wind will find a dull flower as easily as a gaudy one. In self-fertilizing flowers it is also of no use.
Fig. 1
Eighty years ago Sprengel maintained that breeding in and in would be as injurious in the vegetal as in the animal world, and he argued that colors and odors attract insects and thus secure cross-fertilization. It was the largest thought which had ever entered the head of a botanist. But Sprengel was ridiculed in his own generation and
