Fig. 4.—RYE SMUT.
There is one case where this change takes place which you have probably often seen. When I was a child I used to be very fond of getting from the woods close to the house, or from the wood-pile, bits of shining wood and bark, which we called "fox fire." The wood was always old and decaying, and we thought it was shining because it was dying. But really the perishing wood was covered all over with tiny mushrooms, which shone with a light something like the glimmer of a fire-fly. In some countries this brightness is very wonderful. In Australia people have been able to read by the light of a shining stump overgrown with luminous fungi.
Fig. 5.—MILDEW ON VIRGINIA CREEPER.
Some of the fungi have not even the manners to wait until their victims are dead. They take possession of living plants and animals, and never rest until they have destroyed them. The disease among potatoes called the potato blight (Fig. 2), of which we hear so much, is caused by the growth of a little fungous plant in the mouths, or breathing holes, on the skin of the potato, and the blight and mildew (Fig. 3) and smut of wheat and corn and rye (Fig. 4) are all due to the same cause. The mouldy look upon vine leaves is nothing else. I put a leaf of Virginia creeper which looked whitish and ugly under the microscope one day, and found the whole surface covered with a net-work of silvery threads, with a wonderful, fruit growing upon it. The fruits looked like peeled oranges surrounded with threads of spun sugar, or occasionally like a gigantic blackberry sparkling with crystals. This was only a common mildew, but under the magnifier it seemed a wonderful garden, growing conserves and fairy fruits, and was beautiful, beyond description. (Fig. 5.)
Fig. 6.—SILK-WORM FUNGUS.
The silk-worm is attacked by a fungous plant (Fig. 6). It takes possession of the worm just before it begins to spin its cocoon, and some years ago it destroyed such multitudes that the French silk trade was seriously threatened. The microscope was again brought into use, and the cause of the trouble discovered, and the cure effected.
The untiring Pasteur studied up this and other diseases of the silk-worm as he did those of wine and beer, and helped the silk-worm growers to stamp out the disease when it appeared. It perhaps seems a small thing for a man of genius like Pasteur to give his whole life to studying these little plants through the microscope, but never was a life more helpfully and patriotically spent. Hundreds of thousands of the French peasants depended for daily food and shelter upon what they earned in the wine and beer and silk trades, and these trades Pasteur's work has saved from destruction or great loss. It has been said that his work with the microscope has saved to France more than the awful French Revolution cost her.