For the variety of color observed among flowers there appear to be two principal reasons. A little reflection will show that, since flowers are so dependent on insects for the conveyance of their pollen, it must be to the advantage of each species of plant to possess flowers distinctively colored and capable of being easily recognized by honey-seeking insects. A bee does not visit all flowers indiscriminately; it would be greatly to the flowers’ disadvantage if it did. In the course of a single journey the bee for the most part restricts itself to the flowers of one species, and has been known to visit as many as thirty dead-nettles in succession, passing over all other flowers. Time is saved by this method, for by keeping to one kind of flower at a time the insect becomes familiar with its outs and ins, and the practice thus acquired enables it to overtake a larger number of blossoms than it could if it did not observe this rule. This constancy in visiting the same kind of flower is of great importance to plants, since it ensures that the pollen will be conveyed to a flower of the same species as that from which it came. But if all flowers were colored and perfumed alike, the winged botanist could not identify the species; the pollen would be constantly transferred to the stigmas of the wrong flowers, where it would be useless, and so the work of cross-fertilization would be seriously impeded. A second cause contributing to the variety observed among flowers is the desirability of attracting special kinds of insects. As we have just seen, an insect does not visit all kinds of flowers indiscriminately; neither, on the other hand, does a flower attract indiscriminately all kinds of insects. Not only are injurious and unprofitable visitors excluded, but the more specialized insects are in greatest demand. Partiality for particular insects is shown both by the shapes and coloring of flowers. Open shallow flowers, with exposed honey accessible to almost all insects, have, as their most frequent visitors, short-lipped flies and beetles. Many blossoms, again, have become specially adapted to bees. Their honey is placed beyond the reach of short-lipped fliers, and requires the slender proboscis of a bee or butterfly for its extraction. Honeysuckle, habenaria, plumbago, phlox, and narcissus illustrate a third type, with flower-tubes so narrow and deep that their nectar is quite inaccessible even to bees, and is reserved entirely for moths and butterflies, which possess an extremely long and thin proboscis. There is a corresponding adaptation in the colors; the gay tints of the buttercup, poppy, and rose appear to have special attractions for beetles; bees show a decided preference for blue, and this color predominates in flowers whose shapes are adapted to their visits. Deep tubular flowers specialized for Lepidoptera fall into two divisions, according as they solicit the attentions of diurnal butterflies or nocturnal moths.