Diseases of deciduous forest trees Diseases of deciduous forest trees diseasesofdecidu00vons Year: 1909 54 DISEASES OF DECIDUOUS FOREST TREES. MANNER OF INFECTION. One of the most practical questions in connection with the decay of sapwood of broadleaf species, as well as of conifers, deals with the manner in which the sapwood becomes infected with the fungus. With the possible exception of some of the fungi referred to in a pre- vious part of the bulletin, such as Fomes igniarius and Polyporus sulphureus, most of the fungi which bring about the decay of struc- tural timber do not grow in li
Diseases of deciduous forest trees Diseases of deciduous forest trees diseasesofdecidu00vons Year: 1909 54 DISEASES OF DECIDUOUS FOREST TREES. MANNER OF INFECTION. One of the most practical questions in connection with the decay of sapwood of broadleaf species, as well as of conifers, deals with the manner in which the sapwood becomes infected with the fungus. With the possible exception of some of the fungi referred to in a pre- vious part of the bulletin, such as Fomes igniarius and Polyporus sulphureus, most of the fungi which bring about the decay of struc- tural timber do not grow in living trees. The heart wood of the liv- ing tree is accordingly free from the supposed germs of decay, and wherever any decay does take place the spores of the fungi responsi- ble for the same must get into the wood from the outside. Although this has been very definitely shown to be the case, there is still a very widespread belief among timbermen that decay starts in the interior of the stick. This has arisen from the fact that pieces Fig. 11.—Cross section of an oak railroad tie rotted by one of the sap-rot fungi. Note the season crack through which the fungus obtained entrance to the interior. of wood may appear perfectly sound on the outside and still may be wholly decayed in the inner part. In figure 11a striking example of this is shown. This figure shows a section taken from a piece of 'bottom' red oak cut in Ma}', 1904. The timber was piled in the open, and the section here shown was taken in 1906. It will be noted that the outer quarter of an inch of wood appears perfectly sound and that immediately inside this sound layer the wood has been completely decayed. There was absolutely no external sign on this timber which would indicate that it was not sound throughout. Instances of this kind are numerous and they naturally give rise to much apprehension on the part of the purchaser of timber, because it is not practicable to cut into timbers for the purpose of deter-
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