Page:Popular Science Monthly Volume 39.djvu/83

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73
MY GARDEN ON AN ONION.

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.

PSM V39 D083 Penicillium glaucum.jpg
Fig. 1. — Penicillium glaucum.

The ends of these 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,