Popular Science Monthly/Volume 39/May 1891/My Garden on an Onion



THERE was one great difference between this garden of mine and the gardens of my neighbors—an enormous difference, I might say—for, while they had onions in their gardens, my garden was on an onion. In fact, the onion was my garden, and in some respects this was an advantage to me. I had no soil to prepare, no seed to sow. I had merely to keep my onion a little moist, and the crops appeared of themselves.

The first to come was a sage-green down, appearing near the neck of the onion, just where the clear, shining scales close round the stalk. If the onion were put into the earth, this stalk would shoot straight up and bear a crown of flowers, followed by a crop of onion seed. It makes efforts to sprout even in a dark cellar. It pushes the scales apart, and the last remnant of life leaves them—of their own life, I mean, for, no sooner are they dead, than a host of tiny spores find life-food in their remains. These spores had been falling on my onion scales for months, but, so long as the scales were unbroken, could gain no roothold. Now thousands of them had pushed out little threads, which, branching and interlacing with each other, at last formed a film that the eye could see. Then quickly followed the sage-colored, velvety spots, and I knew that my first crop was ready for examination.

What was it?

The housekeeper called it mold. She said that my onion "had begun to get moldy." Mold is one of her deadly enemies. She recognizes it as a sign of rot or decay, and, wisely from her point of view, she gets rid of it as quickly as possible. I called it mold also—a mold. For I knew that before long there would appear other crops unlike this one, yet like enough to bear the name of mold also. I knew, too, that though these molds are almost too small to be seen by the naked eye, they have Cousins that every one knows by sight. There are the mushrooms, the toadstools—yellow, red, and brown—the gigantic puff-balls, and many an odd-looking mass simply called "a fungus." The term fungus, or more often its plural form fungi, denotes a most persistent, industrious class of plants whose one aim in life is the production of millions and millions of spores. The sage-green spots on the neck of my onion were the spores of a fungus. With a needle I could scatter them like a cloud of fine powder. But I could not see how they were growing on the little plants without a microscope that would magnify them about three hundred times.

With such a microscope I saw transparent, branching, interlacing threads, called hyphæ, and thousands of loose spores. Many of the threads ended in little tassels. These tassels I found to he formed in a very interesting manner. First, the creeping hyphæ, send branches into the air. Then these branches bear each three or four branchlets. From the ends of the branchlets grow a number of fine, parallel threads called sterigmata. The ends of these Fig. 1.—Penicillium glaucum. sterigmata contract and form little round, bead-like bodies commonly known as spores. As they are, however, actual bits of the branching hyphæ—bits exactly like the rest of the hyphæ in their constitution—they have no right to be called spores. The name conidia has, therefore, been made for them, from a Greek word meaning dust. As soon as each of these conidia or dust-like bodies is completed, another forms behind it, a third behind the second, and so on; the first being thrust forward until at last it is pushed off altogether and falls. The second shortly follows it, and then the third, and so the process goes on, old conidia falling off at one end and new ones forming at the other. It is these strings of conidia that give the tassel-like look to the ends of the aërial hyphæ. To the botanists who first studied them they suggested little brushes; the brushes that artists call pencils—camel's-hair pencils, for instance. The Latin name for brush being penicillum, this "brush"-bearing fungus received the name of Penicillium. Moreover, to distinguish a Penicillium with sage-green brushes, a second name, glaucum, was found. The first crop to appear on my onion was, thus, Penicillium glaucum, a fungus by no means confined to onions. My housekeeper has taken felted masses of it out of her cans of fruit; has bewailed its sage-green conidia on her jam, and even on her bread and pies. Indeed, she has to keep a sharp lookout for them, never knowing where they may next appear. I can only tell her that the air is full of them, and that they settle here, there, and everywhere, and will surely grow wherever they find moisture and nourishment to suit them.

The next crop that my onion bore made grayish patches on the outermost of those juicy layers, the bases of last year's leaves. With the eye alone I could make out the separate little plants, and, when I held a magnifying glass over them, it was like looking down on a fairy forest of brown-stemmed, branching trees covered with a luxuriant, silvery foliage. In this miniature tree I recognized a mold called Polyactis (many-branched), a fungus that is sure to show itself, sooner or later, on decaying vegetables. To remove one of the little trees and place it under the microscope required as much patient care as I could muster; for not only does the Polyactis take a firm hold of the leaf-base with its spreading, root-like hyphæ, but at the least jar it sheds its foliage, branches and all, and nothing remains but an uninteresting, pointed stem. Yet, if we could continuously watch this stem for a day Fig. 2.—Polyactis cinerea. or so, it would prove anything but uninteresting. Almost at once the protoplasm stored within it begins to form other branches as luxuriant as those that fell. When each is furnished with a due amount, a partition cuts it off from the main supply. Henceforth it rests merely upon the parent stem. It sends out branches on its own account, and gradually gives over its protoplasm to them. These branches fork and fork again, until at last the protoplasm is all concentrated in the ends of tiny branchlets, which swell and sprout all over with little points or sterigmata. Each little point contracts and then swells at the end to form an oval, bladder-like body. It is these oval bodies that give the look of foliage to the Polyactis, and as soon as they have received the whole nourishment of the branchlets they cut themselves off from their sterigmata and hang together in a grape-like cluster. These are the conidia that it has been the business of the whole plant to produce, and, in order that more may be borne by the same stem, they must speedily fall and carry the empty branches with them.

The third crop appeared where I least expected to see it—on the heads of my Polyactis. First of all, fine, silvery lines ran from one Polyactis tree to another, looking, through the magnifying glass, like part of some complicated system of telegraph wires. In a day or two they formed a perfect network, on which pink dots began to appear. The dots increased in number, and soon the Polyactis was completely covered with a pinkish film. The film was pretty in itself, and I was forced to admire it, although I regretted the untimely extinction of my Polyactis. Shortly, however, it turned a dingy brown and fell to the onion, crushing the Polyactis under it. The conidia of the Polyactis germinated, and sent up another crop of tiny trees; but they had not run their little cycle of changes long, before the fine white lines appeared among them. The pinkish film followed, and then, again, film and Polyactis fell to the onion in a dirty-looking mass. The Polyactis took a fresh part of the leaf-base; the pink film followed it. Polyactis tried the inner side of the leaf-base; the film found it even there. The Polyactis crept up the sprouts that had burst through the scales; the film still pursued it—in fact, the Polyactis could grow nowhere on this onion without being overrun by the silvery threads. For days I watched the strife with naked Fig. 3.—Polyactis overrun by Baryeidamia parasitica. eye, magnifying glass, and microscope, and saw the Polyactis gradually succumb and the onion itself rot and blacken under the repeated attacks of the pink-dotted film.

The microscope showed the film to be a tangle of fine, transparent hyphæ, and the pink dots little balls containing spores. Very beautiful are these Baryeidamia spore-balls, changing, as they mature, from pink to a rich seal brown, and surrounded always with clear, scalloped edges. In such profusion, also, are they produced that hundreds of them may be taken up at once on the point of a needle.

Though the most successful, these were by no means all the crops that my onion bore; at least three other minute fungi struggled for existence, but could gain no headway against the pink-filmed Baryeidamia. These, like the Penicillium, Polyactis, and Baryeidamia itself, were all of a comparatively harmless kind. They were merely scavengers, seeking their living on parts of the onion already dead, and thriving on material that it no longer had power to use. The onion, however, had nourished at least one fungus of a very different nature. My microscope showed me its clear, crescent-shaped conidia, and in the tissues of the leaf-bases its hyphæ were creeping from cell to cell, stealing the nourishment prepared for next year's sprouts. This fungus is a thief preying on the industry of the onion—it is more than a thief, for its ravages leave destruction and death in their wake.

The warmth and moisture necessary for the growth of my crops were not good for the onion. It developed untimely, sickly sprouts from the interior layers, while the exterior became the prey of swarms of those minute forms of life known as bacteria—forms that lie, as it were, in the border-land between plant life and animal, and whose function it is to resolve complicated organic structures into their original elements. Under this process my onion sank into a mass of putrescence so ill-looking and ill-smelling that, ere its original elements were reached, I committed it to the swifter dissolution of the flames.