DISEASES OF TREES FROM MECHANICAL INJURIES. 161 



of dissolving the walls of the sound plant cells, even if they do not in the 

 beginning possess this power. Aided by the increased moisture, which is 

 favored by the presence of a damp, earthy layer on the surface of the 

 wound, the destructive threads make their way slowly along the interior of 

 the trunk, the process of destruction causing an increase of moisture and 

 sliminess, which only makes the ultimate destruction of the hitherto sound 

 wood the more certain. While all this is going on within the trunk there 

 may be no definite indication on the outside of the harm done. The toad- 

 stools, as we call them, are the fructification of the fungi, of which the 

 threads are the organs of vegetation, and it is not until after the latter 

 have attained a somewhat advanced development that the toadstools them- 

 selves appear on the surface. Their appearance almost invariably indi- 

 cates not that trouble may be expected, but that the disease has already 

 made considerable progress. 



The toadstools and punk-fungi, of which I have spoken, are usually not 

 limited in their growth to any one species of tree, but may grow on a good 

 many different kinds. There are some species, however, which attack only 

 particular kinds of trees, and among the number are forms which are more 

 virulent and rapid in their action, especially those that attack the roots 

 when they are wounded. It is not my purpose, nor would the limited 

 time allow me, to give an account of these special parasites. Enough, 

 however, has been said to demonstrate the danger of open wounds and the 

 necessity of aiding nature in her efforts to heal them. In the natural 

 course of events many wounds must occur from the violent action of the 

 wind and snow, and we should do what we can to remedy them. But it is 

 perhaps more to the purpose that, recognizing the danger, we should use 

 our influence to prevent the avoidable and wilful maiming of our shade 

 trees by careless and ignorant people. 



So far as the treatment of wounds is concerned, our object should be to 

 cover the exposed surfaces, so that moisture, which would cause them to 

 rot, may be excluded, and that the spores of fungus parasites may not find 

 an entrance. A useful hint as to what should be done is given us by nature 

 herself. In some respects the coniferous trees suffer less from wounds 

 than other trees. The reason is that in the wood of conifers there are 

 canals or passages which contain resinous substances, and when the wood 

 of such trees is wounded they exude and form a close varnish of resin over 

 the exposed surfaces, which are thus kept dry and protected from weather- 

 ing. As a result, the wood is less likely to rot than in the case of other 

 trees whose wood contains no resin. The trees of the latter description, 

 when wounds occur by accident or design, the indication, to use a medical 

 expression, is to coat the cut surface with tar or some similar substance. 

 There are several practical considerations to be borne in mind in applying 

 the tar. If the wounded surface is rough and splintered, it should in the 

 first place be made as smooth as possible, and where branches have been 

 broken off a few inches from the axis from which they sprung, they should 

 be sawn off close down to the main axis. 



When branches are to be pruned, it is of importance that it should be 

 done at the right season. It might be inferred from what was said pre- 

 viously that the summer months would be the best time, because the cam- 

 bium is then active and the callus begins to form at once. There are, 

 however, other points to be considered. Unless the branch is small, it will 

 take several years for the callus to cover the whole wound, and, mean- 

 while, the exposed wood may rot unless well coated with tar. The import- 



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