The Angraecum also affords in this long pendent nectary a most lucid illustration of the present workings of natural selection. The normal length of that nectary should be about eleven inches, but in fact this length varies considerably in the flowers of different plants, this tendency to variation in all organic life being an essential and amply demonstrated postulate of the entire theory of natural selection. Let us suppose a flower whose nectary chances to be only six inches in length. The moth visits this flower, but the tip of its tongue reaches the nectar long before it can bring its head into the opening of the tube. This being a vital condition, the moth fails to withdraw the pollen; and inasmuch as the pollen is usually deposited close to the head of the moth, this flower would _receive_ no pollen upon its stigma. This particular blossom would thus be both barren and sterile. None of its pollen would be carried to other stigmas, nor would it set a seed to perpetuate by inheritance its shorter nectary. Again, let us suppose the variation of an extra long nectary, and the writer recently saw a number of these orchids with nectaries thirteen inches in length. The moth comes, and now must needs insert its head to the utmost into the opening of the flower. This would insure its fertilization by the pollen on the insect's tongue; and even though the sipper _failed_ to reach the nectar, the pollen would be withdrawn upon the tongue, to be carried to other flowers, which might thus be expected to inherit from the paternal side the tendency to the _longer_ nectary. The tendency towards the perpetuation of the short nectary is therefore stopped, while that of the longer nectary is insured. _THE MILKWEED_ The singular hospitality of our milkweed blossom is nowhere matched among Flora's minions, and would seem occasionally in need of supervision. Just outside the door here at my country studio, almost in touch of its threshold, year after year there blooms a large clump of milkweed (_Asclepias cornuta_), and, what with the fragrance of its purple pompons and the murmurous music of its bees, its fortnight of bloom is not permitted to be forgotten for a moment. Only a moment ago a whiff of more than usual redolence from the open window at which I am sitting reminded me that the flowers were even now in the heyday of their prime, and the loud droning music betokened that the bees were making the most of their opportunities. Yielding to the temptation, I was soon standing in the midst of the plants. The purple fragrant umbels of bloom hung close about me on all sides, each flower, with its five generous horns of plenty, drained over and over again by the eager sipping swarm.