A good illustration of the workings of insect pollination may be found in the sweet pea, or in any member of the pea family. The flower has a rough resemblance to a butterfly, whose projecting body is represented by a structure like the keel of a boat. In this keel is a cluster of stamens, and also the pistil with its stigma at the top. While lying in this keel the stamens shed their pollen upon the style, which usually has hairs or some sticky surface to receive it. Accordingly the style bears the stigma on top and masses of pollen stuck to its sides below. An insect being attracted to such a flower naturally lands upon the keel as upon a shelf, with its head toward the center of the flower, where the nectar is deposited. If the insect is heavy enough the weight of its body pushes down the keel, but the contained style is anchored, so that it seems to dart out, and strikes the insect's body, first with the stigma at the tip, and then glancing along rubs its side against the body of the insect. The insect flies away with pollen rubbed upon its body, and when it goes through the same performance at another flower, the new stigma strikes it first and gets some of the pollen, and then some more pollen is smeared on, and so the pollen is carried from one flower to the stigma of another flower. It is easy to see the effect of the weight of a heavy insect by pressing down the keel with a pencil, when the style will be seen to dart forth at the tip. Perhaps one of the most common ways of securing pollination is that in which the pollen and stigma are not ready at the same time in the same flower. The pollen may be ready to shed, but the stigma is not ready to receive, or the reverse may be true. This would seem very effective in preventing self-pollination. Illustrations of this kind are exceedingly numerous, but perhaps as common a one as any is furnished by the great fireweed, Epilobium. It has a conspicuous purple flower, and if a patch of the plants be examined the flowers will be found in two conditions. In one set the cluster of stamens will be found projecting straight out from the flower, while the style with its stigma is turned back out of the way under the flower. In the other set the stamens, having shed their pollen, are turned back behind the flower, while the style has straightened up, and the mature stigma holds the same position that the anthers did the day before. An insect, in visiting such a group, therefore, may fly straight towards a flower whose stamens are projecting and shedding, and its body will be dusted with the pollen. If it now flies to a flower which is a little older, whose stamens are out of the way, but whose style is projecting, its body carrying the pollen will strike the stigma. In this way the pollen is very effectively transferred from one flower to another.