. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 164 BOTANY the bark from any tree infected with bracket fungus, and you will find the silvery threads of the mycelium sending their greedy hyphae to all parts of the wood adjacent to the spot first attacked by the fungus. This fungus begins its life by the lodgment of a spore in some part of the tree which has become diseased or broken. Once established on its host, it spreads rapidly. There is no remedy except to kill the tree and burn it, so as to burn up the spores. Many fine trees, soun
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 164 BOTANY the bark from any tree infected with bracket fungus, and you will find the silvery threads of the mycelium sending their greedy hyphae to all parts of the wood adjacent to the spot first attacked by the fungus. This fungus begins its life by the lodgment of a spore in some part of the tree which has become diseased or broken. Once established on its host, it spreads rapidly. There is no remedy except to kill the tree and burn it, so as to burn up the spores. Many fine trees, sound except for a slight bruise or other injury, are annuallj'" infected and eventually killed. In cities thousands of trees become infected through careless hitching of horses so that the horse may gnaw or crib on the tree, thus exposing a fresh surface for the growth of spores. Field Work. — A field trip to a park or grove near home will show the great destruction of timber by this means. Count the number of perfect trees in a given area. Compare with the number of trees attacked by the fungus. Does the fungus appear to be transmit;ted from one tree to a tree near at hand ? In how many instances can you discover the point where the fungus first attacked the tree ? Parasitic Fungi. — Of even more importance are the fungi that attack a living host. The most important of such plants from an economic standpoint are the rusts, smuts, and mildews which prey upon grain, corn, and other cultivated plants. Some of these are also parasitic upon fruit and shade trees. Damage ex- tending to hundreds of millions of dollars is annu- Corn smut, a fungus parasitic on corn; the black „ii„ Afxnc^ hir f Itaqa -nlanf« mass consists almost entirely of ripe spores. ^^V ^^'^^ ^y Lnese pidms. Wheat Rust.—Wheat rust is probably the most destructive parasite in the world. For hundreds of years wheat rust has been one of the most dreaded of plant diseases, because it destroys the one harve
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