Mix freshly-boiled and strained juice of stewed fruit (preferably colourless or nearly so) with an equal quantity of water. Half fill a small glass with the mixture, and with the point of a needle add a few spores from the mould on the bread. Cover the glass, avoid shaking it, and examine day by day. Notice the delicate threads (hyphae) of the mycelium which spreads over the liquid and sends down branches below the surface. Observe also the hyphae which grow up into the air and bear spore-knobs at the end. Similarly, sow some of the spores on a little of the nutritive solution of salts (p. 27) contained in a clean glass. Do these spores also develop into moulds? Why not? Scratch through the skin of a ripe fruit (e.g. plum, apple, grape, etc.) with a needle, and lay the fruit aside with the scratch upward. Scratch a similar fruit in the same way, and rub into the scratch a few mould-spores before laying it aside. With these put a third fruit which has a perfectly whole skin. Compare the fruits after a few days. 3. Blue mould (Penicillium).—After some days the white mould on the bread will probably be crowded out by a blue or greenish velvety mould called Penicillium. Examine it with a lens. As with Mucor, make experiments as to the action of light upon this mould; the [Pg 208] germination of its spores (which form a greenish powder on the ends of the short aërial hyphae) in fruit-juice; and the action of the spores upon ripe fruits. Common moulds.—In the dust floating about in the air the spores of certain moulds are almost always present. When these spores fall upon materials which—like bread, fruit, old leather, etc.—are capable of affording them suitable food-substances, they germinate and form the woolly growths which are familiar to everyone.