The experiment with the lavender-oil, naphthaline and the rest would therefore seem to prove that odour proceeds from two sources. For emission substitute undulation; and the problem of the Great Peacock is explained. Without losing any of its substance, a luminous point shakes the ether with its vibrations and fills a circle of indefinite width with light. This must almost express the working of the mother Bombyx’ tell-tale discharge. It does not emit molecules: it vibrates; it sets in motion waves capable of spreading to distances incompatible with a real diffusion of matter. In its entirety, smell would thus seem to have two domains: that of the particles dissolved in the air and that of the ethereal waves. The first alone is known to us. It belongs also to the insect. It is this which informs the Saprinus of the dragon arum’s fetidity and the Silpha and Necrophorus of the stench of the Mole. The second, which is far superior in its range through space, escapes us altogether, because we lack the necessary sensory equipment. The Great Peacock and the Banded Monk know it at the time of the nuptial rejoicings. And many others must share it in various degrees, according to the exigencies of their mode of life. Like light, odour has its X-rays. Should science one day, instructed by the insect, endow us with a radiograph of smells, this artificial nose will open out to us a world of marvels. CHAPTER XIV THE CABBAGE-CATERPILLAR The cabbage of our modern kitchen-gardens is a semi-artificial plant, the produce of our agricultural ingenuity quite as much as of the niggardly gifts of nature. Spontaneous vegetation supplied us with the long-stalked, scanty-leaved, ill-smelling wilding, as found, according to the botanists, on the ocean cliffs. He had need of a rare inspiration who first showed faith in this rustic clown and proposed to improve it in his garden-patch. Progressing by infinitesimal degrees, culture wrought miracles. It began by persuading the wild cabbage to discard its wretched leaves, beaten by the sea-winds, and to replace them by others, ample and fleshy and close-fitting. The gentle cabbage submitted without protest. It deprived itself of the joys of light by arranging its leaves in a large, compact head, white and tender. In our day, among the successors of those first tiny hearts, are some that, by virtue of their massive bulk, have earned the glorious name of chou quintal, as who should say, a hundredweight of cabbage. They are real monuments of green stuff. Later, man thought of obtaining a generous dish with the thousand little sprays of the inflorescence. The cabbage consented. Under the cover of the central leaves, it gorged with food its sheaves of blossom, its flower-stalks, its branches and worked the lot into a fleshy conglomeration. This is the cauliflower, the broccoli.