With the spores of this mould repeated sowings have been made, with gratifying results. When a slice of fresh bread was placed in the bell-jar and certain marked places were sprinkled with spores by means of a pair of forceps, in the course of twenty-six hours those spots sown were covered with the young mould, while all other places were entirely free from it. In one case a fresh slice of bread was wrapped in a piece of paper, with the exception of a star-shaped figure cut from the paper, which came in the middle of the slice. Over the whole a slice of mouldy bread was shaken so gently that no spores were seen to fall; the paper was then carefully removed, and the bread placed under the bell-jar. After the usual time a fine star of blue mould made its appearance, soon spreading over the whole of the bread. One could as easily write his name in mould on bread as with clover-seed upon the soil, though it would not be as enduring an inscription.
It seems difficult for some people to see how the spores of these various moulds can exist almost everywhere, ready to grow when the first opportunity offers itself. With the hope of making this matter appear clearer, the following calculations have been carefully made: The blue mould (Penicillium crustaceum) is very favorable for the estimation of the number of spores produced, as the heads are quite open, and the spores are naked and distinct.
Fig. 8.—Tricothesium roseum. Fr.
A piece of decaying apple was selected, because the mould can be removed from that portion covered with the smooth skin without being mixed with foreign matter. When the mould was still young and no spores had fallen away, it was viewed with the high power of the microscope. There were usually twenty filaments to each head, and twenty spores on a filament, or 4,000 spores to a head or single stalk.
