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are girdled the fungus continues to grow extensively through the dead bark, sometimes covering the entire surface with reddish brown pustules. These pustules produce mostly the type of spores called ascospores, although occasionally long strings of conidia are also produced, even on bark that has been dead at least a year. If the proper conditions of moisture are present the fungus will continue to grow on the bark of chestnut logs and even upon bare wood.
When a branch or trunk is girdled the leaves above change color and sooner or later wither. (Pl. XXXVII.) These prematurely killed leaves often remain on the branches, forming, together with the persistent burs, the most conspicuous winter symptom of the disease. The most conspicuous symptom at all times of the year is the occurrence of sprouts at the base of the tree, on the trunk, or on the branches. (Pl. XXXV; Pl. XXXVI, figs. 1 and 2; also Pl. XXXVII.) Sprouts may appear below every canker on a tree, and there are often many such cankers. These sprouts are usually very luxuriant and quick growing, but rarely survive their second or third year, as they in turn are killed by the fungus. The age of the oldest living sprout, as determined by the number of its annual rings, is an indication.of. the minimum age of the canker immediately above. The annual development of sprouts from the base of a tree sometimes continues vigorously for at least six years after the tree is dead, which fact affords clear evidence of the healthy condition of the roots. If infection of these basal sprouts could be prevented, they would develop into a much better type of coppice than is usually seen, since they are rooted in the ground. After the tree is dead the dead sprouts, together with the scars left by cankers on the outer layers of wood, serve to show what killed the tree long after the bark has completely decayed and fallen away.
The fungus apparently does not penetrate to any considerable distance below the ground; nor does it attack the green leaves or the greenest of the young wood. Late in the season it will readily attack wood of the current year. This is observed, however, most commonly on sprouts.
Regarding the virulent parasitism of Endothia parasitica there is no possible question. It is easy to demonstrate this by making artificial inoculations in healthy trees. Plate XXXVII shows such an inoculated tree. The conidia, or so-called summer spores of the fungus, were put into a slit in the bark near the base of this little potted chestnut tree and a canker promptly developed. The typical symptoms of the bark disease, as they occur in large trees, followed-girdling of the trunk, withering of the leaves above, and prompt development of sprouts from below the canker. Some weeks after the photograph (Pl. XXXVII) was taken the sprouts were all killed by the downward growth of the canker.
MEANS OF SPREAD AND INFECTION.
Recent investigations show that the ascospores are commonly ejected during and after a rain, and on account of their small size may be blown by the wind for a distance of at least 50 feet, in spite of their sticky character. The strings of sticky conidia are instantly 'dissolved by rain, and are washed down over the surface of the tree. It is conceivable that they may be blown by the wind as far as rain or spray is blown or, mingling with dust at the foot of the tree, be blown about with the dust. There is strong evidence that the sticky conidia and ascospores may become attached to the various forms of animal life-insects, birds, squirrels, etc.-which frequent the diseased trees, and so be carried by them to other trees. That the disease is carried bodily for great distances in diseased chestnut nursery stock, unbarked ties, poles, or other timber, tanbark, etc., is a demonstrated fact.
When the spores have once been carried to a previously uninfected tree they may develop in any sort of wound or injury in the bark that is reasonably moist, and produce a canker. There is, indeed, some slight evidence that under certain conditions the fungus may gain entrance through apparently uninjured bark; but it is not necessary to assume that such entrance is common in nature, for the bark of the typical chestnut tree is covered with all sorts of injuries through which the fungus can readily find entrance.
No evidence has been adduced up to the present time to show that a tree with reduced vitality is more susceptible to infection or that the cankers develop more rapidly in such a tree than in a perfectly healthy and well-nourished tree of either seedling or coppice growth, except in those cases where such reduced vitality is accompanied by bark injuries through which spores can gain entrance. Nor has any evidence yet been adduced to show that weather or soil conditions within the present range of the disease exert any appreciable effect upon it, beyond the fact that wet weather in general favors the distribution of the spores.
The American chestnut, the chinquapin, and the cultivated varieties and hybrids of the European chestnut are all subject to the bark disease, although apparently varying in susceptibility. The Japanese, Korean, and Chinese varieties appear to show decided resistance. Unfortunately, these varieties are, so far as known, too small to be of value except as lawn and nut-producing trees. In America true examples of these varieties are rarely seen. What passes in the market as the Japanese chestnut, for example, is almost invariably a hybrid between the Japanese and some American or European variety.
Recently Endothia parasitica has been reported on three species of oaks. Although such occurrence appears to be rare, the spread of the bark disease to oak trees presents an unpleasant possibility.
LINES OF INVESTIGATION AND CONTROL.
The history of the investigation of the chestnut bark disease with reference to its control is a long story of procrastination. Undoubtedly present on Long Island in the nineties and doing conspicuous damage in the largest city of the United States as early as 1904, the disease is, nevertheless, not mentioned in scientific literature until 1906. It is not mentioned in any economic publication until 1908, and then without any appreciation of its seriousness. The impression was allowed to prevail that the disease was due to weather conditions and would soon disappear of itself, and hence was not worthy of serious attention. So in attempting control of the disease we find ourselves handicapped at every step by lack of knowledge, although there would have been ample time to secure this knowledge if practical investigations had been begun even as late as when Merkel noted the serious character of the disease.
CUTTING OUT ADVANCE INFECTIONS.
Many scattered advance infections have been cut out, including all of those in Pennsylvania. That State has taken the lead not only in cutting out advance infections and utilizing dead chestnut trees, but also in all lines of investigation of the disease. The results of this work are awaited with profound interest, not only by such States as Ohio and West Virginia, which are in part protected by the action of Pennsylvania, but also by those more distant Southern States that still have time to profit by the experience of Pennsylvania.
UTILIZATION OF DEAD AND DYING TREES.
The utilization of dead and dying trees is a forestry problem of the utmost importance. In the neighborhood of New York City all chestnut trees are dead; as we go from there in any direction we find areas of dead trees, corresponding to old points of advance infection, surrounded by more recently infected trees. Between these areas are occasional "islands" of still healthy trees. But the number of trees that should be immediately utilized is enormous and will increase annually. They should be used to save the timber, to reduce infection, and to prevent possible increase of injurious insects. Since the wood of a diseased tree is rotted only immediately under the cankers, a tree that is cut promptly may be expected to make practically as good timber as a sound tree. However, if
cutting is delayed until long after the tree is girdled, the timber will necessarily be open to the same objections as that from any dead tree.
The Pennsylvania Chestnut Tree Blight Commission has induced certain railroads in that State to make a discrimination in freight rates in favor of products from diseased chestnut trees, which enables these products to be used more cheaply than those of other species. Unless some such plan can be brought about in other States also, it is difficult to see how a great glut in the market for chestnut products can be avoided.
IMPROVEMENTS IN FOREST MANAGEMENT.
The work on the bark disease in certain States has been made the occasion of a general forest survey. Everywhere it will result in more careful management of the surviving trees. In localities where the chestnut is already past saving, this species must be discriminated against. While change of management of chestnut woodland may not affect the course of the disease, except in so far as it involves the cutting out of infected trees, constructive forestry is bound to be stimulated by the work done on this disease. Methods of control of this and other forest diseases, which are visionary now, will be in daily use in 20 years. We do not now realize how rapidly forestry in the Eastern States is becoming as intensive as that of Europe.
The possibility of controlling disease in trees by special fertilization or by direct chemotherapy, that is, by the introduction of chemicals or immunizing substances directly into the tree, has long been a fascinating ideal. The method has been discredited by the number of "fake" remedies which are supposed to be applied in this way. Nevertheless, the basal idea is fundamentally sound. The Pennsylvania Chestnut Tree Blight Commission, in cooperation with the United States Department of Agriculture, is making extensive experiments along this general line. From this work very valuable scientific results are to be expected, whether the method becomes a practical success or not, and the results obtained may be expected to be in some measure applicable to other species of trees, including fruit trees.
BREEDING RESISTANT TREES.
The apparent resistance of various Asiatic chestnuts suggests that if resistant individuals of these varieties are crossed with the American and European chestnuts, hybrids might be produced with the desirable nut characters of one parent and the resistance of the other. So far no resistant individuals of the American chestnut have been found. Trees of both American and Asiatic species of the genus Castanopsis could possibly also be used as resistant parents, at least