. Diseases of deciduous forest trees. Trees. 32 DISEASES OF DECIDUOUS FOREST TREES. of the disease. As stated before, the aspen, the beech, and the but- ternut, in the order given, seem to be the most frequently diseased of all the hosts upon which the fungus has been found. The age of the host tree is probably the most important factor connected with the distribution of the disease. It has been indi- cated that the principal mode of entrance of the fungus is through dead branches. Trees which are not old enough to have many dead branches or which are not old enough to shed their lower branche
. Diseases of deciduous forest trees. Trees. 32 DISEASES OF DECIDUOUS FOREST TREES. of the disease. As stated before, the aspen, the beech, and the but- ternut, in the order given, seem to be the most frequently diseased of all the hosts upon which the fungus has been found. The age of the host tree is probably the most important factor connected with the distribution of the disease. It has been indi- cated that the principal mode of entrance of the fungus is through dead branches. Trees which are not old enough to have many dead branches or which are not old enough to shed their lower branches are free from the disease. When a branch dies and broken off its. is is left to the ex- at- Fig. 4.—An aspen tree with many dead lateral branches; offers a good entrance for wound fungi. each of these wood posed tacks of the fungus. Where trees are very much sup- pressed the fungus may be found on trees only 1 or 2. inches in diameter; but it will be found on examination that such sup- pressed trees are in reality of a consid- erable age. In gen- eral it may be said that none of the common deciduous forest trees are af- fected with the white heart-rot be- ^ fore they are 20 of and years or age, most of them will not become affected until they are considerably more than 20 years old. The aspen and the butternut become infected after they are 20 to 25 years of age. This is especially true of the aspen, on winch dead branches remain on the lower part of the tree trunk for years after they are dead (fig. 4). A clean-stemmed forest of beech stand- ards will show far less susceptibility when 50 to 60 years old than a similar stand in which the dead branches stick out in large num- bers from the lower portions of the trunk. 149. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Von Schrenk, Hermann, 1873-1953; Sp
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