Our common garden salvia shows still another type of flower, which is tubular and irregular (Figure 41). There is an arching, hoodlike structure at the top overhanging a lower lip. This kind of irregularity is common in thousands of different sorts of plants and, usually, it is a device to insure fertilization of the flower by insect visitors. So necessary are these for pregnancy in many plants, that an orchid, once discovered in Madagascar with a tube eighteen inches deep, puzzled the botanists, who were unable to understand how the plant produced seed in the absence of any known insect with a tongue as long as that. Darwin said at once that such an insect would one day be discovered on that island. Years after, Baron von Humboldt, a German naturalist, found the insect and explained the mystery. Perhaps there is no feature of plant life that shows such an amazing amount of variation as the forms of flowers, and while only a few of the simplest deviations from the normal have been discussed here, it must not be forgotten that this infinite variety is a reflection of the ingeniousness of nature in securing a plentiful supply of seed. Form, color, the secretion of sweetish nectar, the night or day blooming of different kinds of flowers, every device that will make fertilization certain, by the flower itself, by insects, or even by the wind, is used in such prodigal fashion, that we come to see the importance of it to all plants only by a realization of the complexity of it and the provisions against its failure.