346 



FORESTS 



FORESTS 



Nature of the disease fungi and their action. 



Fungi are a low class of plants, consisting of 

 fine threads, called hyphae, many hyphae forming 

 the mycelium. The mycelium grows in the dead or 

 living parts, extracting certain food substances 

 therefrom. After varying 

 periods, fruiting bodies are 

 formed, which develop 

 spores. These fruiting bod- 

 ies have various shapes, 

 varying from microscopic 

 structures to the large 

 punks or toadstools so com- 

 monly found on older trees. 

 The spores are discharged 

 into the air, and are dis- 

 tributed from one tree to 

 another by the wind ; they 

 are also carried from tree 

 to tree by insects, rain, or, 

 when the fungi grow under 

 the ground, by burrowing 

 animals, such as moles and 

 mice. 



When the fungus causes 

 a disease of the leaves or 

 branches, the spores usu- 

 ally germinate directly on 

 the leaves or branches, the 

 fungus penetrating into the 

 living tissue, and growing 

 there. When the fungus 

 attacks the heart-wood of 

 the tree, the spore must get 

 into some wound. During 

 the early life of the tree 

 these wounds are very few in number, but as a 

 tree grows older many wounds are formed, and 

 the tendency to close these wounds, either by the 

 formation of callus or by the exudation of gum 

 or resin, is very much reduced. Wounds are made 

 by deer and other browsing animals, by wood- 

 peckers, but chiefly by the breaking off of large 

 branches by the wind or snow. Wherever a wound 

 is made, the spores from numerous wood-rotting 

 fungi enter and germinate, and the mycelium of 

 the fungus grows down into the heart-wood of 

 the tree. When it has reached the heart-wood, it 

 grows both up and down in the tree trunk, and 

 results in the partial or total destruction of the 

 wood, as shown in Figs. 492, 493 and 494. When 

 a sufficient amount of nutritiye material has been 

 absorbed from the trunk, a punk or toadstool forms 

 on the outside, bearing new spores, as shown in 

 Fig. 492. Pig. 497 illustrates a different type of 

 injury. It shows the way in which mistletoe forms 

 a " bird's-nest " on lodge-pole pine. 



The fungi that attack leaves and branches are 

 rarely present in sufficient number to kill a large 

 tree, although they may stunt its growth. They 

 are very much more dangerous to extremely young 

 trees. The so-called "damping-ofl" fungi belong 

 to this group, and they are particularly active in 

 seed-beds. As the tree grows older, the wood-rotting 

 fungi become more important, and the older the 



Fig. 493. Effect on wood 

 ot red spraoe by the 

 mycelum of Folyporus 

 horealis. (Pigs. 493, 494 

 are adapted from Bul- 

 letin No. 193, Cornell 

 Experiment Station.) 



tree gets the more liable to disease it becomes. 

 For most kinds of trees, a certain age usually will 

 mean an almost certain attack by one or the other 

 of the wood-rotting fungi, and it is generally well, 

 when such trees are used for lumber, to cut them 

 shortly after this age has been reached. For pines 

 this may be about eighty to one hundred years. It 

 is the latter class of fungi that are of particular 

 interest to the lumberman and forester. 



Some of the important fungi which produce 

 disease in forest trees are the red heart fungus 

 (Trametes pini. Fig. 496), found on all coniferous 

 trees; the false tinder fungus {Polyporus igniarius. 

 Fig. 495), found on beech, apple, oak, poplar and 

 other hardwoods, where it produces a white, soft rot 

 of the trunk ; the sulfur mushroom, which causes a 

 brown rot of many coniferous trees, and also of 

 oak, walnut, cherry and other deciduous trees. 



The fungi that attack hewn timber and produce 

 decay belong to a separate group. The factors 

 which favor their development are, a certain 

 amount of heat, oxygen, water and food supply. 

 Dry wood will last very much longer than green 

 wood. A post set in the ground with its bark 

 removed will outlast one with the bark on. Sap 

 wood is very much more liable to attack than 

 heart-wood. The rate at which different kinds of 

 wood will decay differs, and woods are accordingly 

 classed as long- and short-lived. Long-lived woods 

 are such as white oak, cypress, cedar, chestnut and 

 redwood ; and short-lived woods are such as fir, 

 hemlock, beech, red oak, gum and the soft pines. 



Fig. 494. Disintegration of wood by Polyporus horealis. 



Prevention of disease. 



In forest trees. — The prevention of diseases in 

 forest trees is more or less difficult. The best 

 method of keeping a tree healthy is to remove those 

 conditions which favor disease. Trees should be 

 grown in well-drained, carefully prepared soil, free 

 from previous fungous contamination. Seed-beds 

 in which a disease has started should be sprayed 

 with Bordeaux mixture. Trees that become dis- 

 eased because of the attack of fungi on their 

 leaves or younger branches should likewise be 

 sprayed with various fungicides, notably Bordeaux 

 mixture; this will prevent all mildews and blights, 

 to a greater or less degree. For fungi that attack 

 the heart-wood, careful attention to wounds is 

 advisable. Wherever a branch is broken or sawed 

 off, the exposed surface, wherever practicable, 

 should be coated with some antiseptic substance, 

 preferably coal-tar creosote that has been heated. 

 All wounds should be carefully trimmed, so as to 



