Fig. 113. Magnified Rose Mildew
Fig. 114. A Mildewed Rose
It is also of great importance to decide whether by keeping the spores away we may prevent mold. Possibly this experiment will help us. Moisten a piece of bread, then dip a match or a pin into the blue mold on a lemon, and draw the match across the moist bread. You will thus plant the spores in a row, though they are so small that perhaps you may not see any of them. Place the bread in a damp place for a few days and watch it. Does the mold grow where you planted it? Does it grow elsewhere? This experiment should prove to you that molds are living things and can be planted. If you find spots elsewhere, you must bear in mind that these spores are very small and light and that some of them were probably blown about when you made your sowing. When you touch the moldy portion of a dry lemon, you see a cloud of dust rise. This dust is made of millions of spores.
If you plant many other kinds of mold you will find that the molds come true to the kind that is planted; that like produces like even among molds.
You can prove, also, that the mold is caused only by other mold. To do this, put some wet bread in a wide-mouthed bottle and plug the mouth of the bottle with cotton. Kill all the spores that may be in this bottle by steaming it an hour in a cooking-steamer. This bread will not mold until you allow live mold from the outside to enter. If, however, at any time you open the bottle and allow spores to enter, or if you plant spores therein, and if there be moisture enough, mold will immediately set in.
Fig. 115. A Highly Magnified Section of Diseased Pear Leaf
Showing how spores are borne
The little plants which make up these molds are called fungi. Some fungi, such as the toadstools, puffballs, and devil's snuff-box, are quite large; others, namely the molds, are very small; and others are even smaller than the molds. Fungi never have the green color of ordinary plants, always reproduce by spores, and feed on living matter or matter that was once alive. Puffballs, for example, are found on rotting wood or dead twigs or roots. Some fungi grow on living plants, and these produce plant disease by taking their nourishment from the plant on which they grow; the latter plant is called the host.
The same blue mold that grows on bread often attacks apples that have been slightly bruised; it cannot pierce healthy apple skin. You can plant the mold in the bruised apple just as you did on bread and watch its rapid spread through the apple. You learn from this the need of preventing bruised or decayed apples from coming in contact with healthy fruit.