But it is in the flower itself that we find the most ingenious arrangements to encourage useful and discourage useless visitors, to assist the former to pollinate the flower, and while offering nectar to the welcome guest to deny it to the unwelcome. The first stage in this specialization is that the flower, instead of having its axis vertical, and facing the sky, is turned on its side by the curving of its stalk, and looks out horizontally. The effect of this is to cause a flying insect on approaching the flower to alight in a particular position--namely, on the lowest petal. Following on the adoption of this attitude the next stage in development is seen in the parts of the flower beginning to alter their shape and position relative to each other and often also their colour. Thus, beginning with a quite regular flower, we can arrange a series showing more and more asymmetry. The tendency is generally for the lowest petal to become enlarged and often conspicuously marked, providing a broad, convenient platform on which insects may alight, while the remainder form walls and roof, protecting the important parts within and by their shape, which is often narrowed and tubular behind, barring access to all but chosen visitors. To find a full series illustrating these transformations we do not need to go to plants widely separated in their affinities. In the Buttercup order (_Ranunculaceæ_) alone every gradation may be found. The flowers of the Buttercups themselves are upright and quite regular. In the Larkspur (_Delphinium_) the flower is turned on its side, and a puzzling combination of coloured sepals and petals--five bright blue unequal sepals and a single large purplish petal of peculiar shape with a long hollow spur behind--produces a quite irregular blossom. The process is carried farther again in the Monkshood (_Aconitum_), in whose well-known blue flower the sepals and petals combine to produce a strikingly irregular blossom, with the upper sepal arching over into a great hood protecting the rest of the flower. In such irregular flowers the essential parts--the pollen-producing and pollen-receiving portions, or stamens and stigma--also alter their position and form, and are so placed that an insect, visiting the flower to obtain nectar (which is generally stored at the back, well out of the way), must of necessity receive pollen on its body, and probably deposit pollen on the stigma. To describe the variety and ingenuity of these devices as found in different flowers might well occupy several chapters, and only one or two examples can be quoted here; familiar wild flowers are chosen, and the reader should examine them for himself to understand their structure. In the well-known Pea type, one great petal arches over the flower; two narrow ones stand one on either side; the remaining two stand on edge below, with their margins in contact, enclosing the stamens and pistil. An insect visiting the flower alights naturally on