Molds

Teacher’s Story

It is lucky for our peace of mind that our eyes are not provided with microscopic lenses, for then we should know that the dust, which seems to foregather upon our furniture from nowhere, is composed of all sorts of germs, many of them of the deadly kind. The spores of mold are very minute objects, the spore-cases being the little white globes, not larger than the head of a small pin which we see upon mold, yet each of these spore-cases breaks and lets out into the world thousands of spores, each one ready and anxious to start a growth of mold and perfectly able to do it under the right conditions; almost any substance which we use for food, if placed in a damp and rather dark place, will prove a favorable situation for the development of the spore which swells, bursts its wall and sends out a short thread. This gains nourishment, grows longer and branches, sending out many threads, some of which go down into the nutritive material and are called the mycelium. While these threads, in a way, act like roots, they are not true roots. Presently the tip ends of the threads, which are spread out in the air above the bread or other material, begin to enlarge, forming little globules; the substance (protoplasm) within them breaks up into little round bodies, and each develops a cell wall and thus becomes a spore. When these are unripe they are white but later, they become almost black. In the blue mold the spores are borne in clusters of chains, and resemble tiny tassels instead of growing within little globular sacs.

Molds, mildews, blights, rusts and smuts are all flowerless plants and, with the mushrooms, belong to the great group of fungi. Molds and mildews will grow upon almost any organic substance, if the right conditions of moisture are present, and the temperature is not too cold.

Molds of several kinds may appear upon the bread used in the experiments for this lesson. Those most likely to appear are the bread mold—consisting of long, white threads tipped with white, globular spore-cases, and the green cheese-mold—which looks like thick patches of blue-green powder. Two others may appear, one a smaller white mold with smaller spore-cases, and a black mold. However, the bread mold is the one most desirable for this lesson, because of its comparatively large size. When examined with a lens, it is a most exquisite plant. The long threads are fringed at the sides, and they pass over and through each other, making a web fit for fairies—a web all beset with the spore-cases, like fairy pearls. However, as the spores ripen, these spore-cases turn black, and after a time so many of them are developed and ripened that the whole mass of mold is black. The time required for the development of mold varies with the temperature. For two or three days nothing may seem to be happening upon the moist bread; then a queer, soft whiteness appears in patches. In a few hours or perhaps during the night, these white patches send up white fuzz which is soon dotted with tiny pearl-like spore-cases. At first there is no odor when the glass is lifted from the saucer, but after the spores ripen, the odor is quite disagreeable.

The special point to teach the children in this lesson is that dryness and sunlight are unfavorable to the development of mold; and it might be well to take one of the luxuriant growths of mold developed in the dark, uncover it and place it in the sunlight, and see how soon it withers. The lesson should also impress upon them that dust is composed, in part, of living germs waiting for a chance to grow.