"All these plants begin with a spore or minute colourless cell of living matter (s, Fig. 23), which spends its energy in sending out tubes in all directions into the leaves, fruit, or paste on which it feeds. The living matter, flowing now this way now that, lays down the walls of its tubes as it flows, and by and by, here and there, a tube, instead of working into the paste, grows upwards into the air and swells at the tip into a colourless ball in which a number of minute seed-like bodies called spores are formed. The ball bursts, the spores fall out, and each one begins to form fresh tubes, and so little by little the mould grows denser and thicker by new plants starting in all directions.
"Under the first microscope you will see a slide showing the tubes which spread through the paste, and which are called the mycelium (m, Fig. 23), and amongst it are three upright tubes, one just starting a, another with the fruit ball forming b, and a third c, which is bursting and throwing out the spores. The Aspergillus and the Penicillium differ from the Mucor in having their spores naked and not enclosed in a spore-case. In Penicillium they grow like the beads of a necklace one above the other on the top of the upright tube, and can very easily be separated (see Fig. 22); while Aspergillus, a most lovely silvery mould, is more complicated in the growth of its spores, for it bears them on many rows branching out from the top of the tube like the rays of a star."
Fig. 23.
Mucor Mucedo, greatly magnified. (After Sachs and Brefeld.)
m, Mycelium, or tangle of threads. a, b, c, Upright tubes in different stages. c, Spore-case bursting and sending out spores. s, 1, 2, 3, A growing spore, in different stages, starting a new mycelium.
"I want you to look at each of these moulds carefully under the microscope, for few people who hastily scrape a mould away, vexed to find it on food or damp clothing, have any idea what a delicate and beautiful structure lies under their hand. These moulds live on decaying matter, but many of the mildews, rusts, and other kinds of fungus, prey upon living plants such as the smut of oats (Ustilago carbo), and the bunt (Tilletia caria) which eats away the inside of the grains of wheat, while another fungus attacks its leaves. There is scarcely a tree or herb which has not one fungus to prey upon it, and many have several, as, for example, the common lime-tree, which is infested by seventy-four different fungi, and the oak by no less than 200.
"So these colourless food-taking plants prey upon their neighbours, while they take their oxygen for breathing from air. The 'ferments,' however, which live inside plants or fluids, take even their oxygen for breathing from their hosts.
"If you go into the garden in summer and pluck an overripe gooseberry, which is bursting like this one I have here, you will probably find that the pulp looks unhealthy and rotten near the split, and the gooseberry will taste tart and disagreeable. This is because a small fungus has grown inside, and worked a change in the juice of the fruit. At first this fungus spread its tubes outside and merely fed upon the fruit, using oxygen from the air in breathing; but by and by the skin gave way, and the fungus crept inside the gooseberry where it could no longer get any fresh air. In this dilemma it was forced to break up the sugar in the fruit and take the oxygen out of it, leaving behind only alcohol and carbonic acid which give the fermented taste to the fruit.
"So the fungus-imp feeds and grows in nature, and when man gets hold of it he forces it to do the same work for a useful purpose, for the grape-fungus grows in the vats in which grapes are crushed and kept away from air, and tearing up the sugar, leaves alcohol behind in the grape-juice, which in this way becomes wine. So, too, the yeast-fungus grows in the malt and hop liquor, turning it into beer; its spores floating in the fluid and increasing at a marvellous rate, as any housewife knows who, getting yeast for her bread, tries to keep it in a corked bottle.