Fifth, the nature and degree of resistance of the Asiatic species. Another problem in relation to tree treatment may be added, that is, the relation of spores and mycelium to toxic agents.
The Pennsylvania Commission maintained laboratories during the summer at Charter Oak, Centre County, and at Mt. Gretna, Lebanon County. The latter has been moved to Franklin and Marshall College, Lancaster, for the winter. We have also had a laboratory at the University of Pennsylvania, which has been greatly enlarged this fall.
The number of people who informed us that they had discovered a sure "cure" for the blight made it necessary to obtain an orchard near Philadelphia where all such discoverers were given an opportunity to demonstrate the efficacy of their remedies. It might be noted that in every case the blight is thriving as usual. These cures consisted largely of an injection of a toxic principle by some means into the circulation of the tree. In some cases this was accompanied by a fertilizer of some kind, and this fertilizer may account for the apparently improved condition of the tree in some cases, after such remedies were used, since the growth was increased and the leaves and branches had a healthier appearance. This increased growth has not had any appreciable effect upon the rapidity of spread of the blight mycelium. As the experiments are not officially finished and recorded it is too early to give any further data. Our pathologists have also conducted experiments in this same line but no medicinal remedy or fertilizer has yet been found.
The varying chemical constituents of chestnut trees, principally tannic acid, have often been suggested in regard to the origin and spread of the blight. Investigators are now working along this line and we hope, for valuable results before long.
The origin of the disease, as already stated, is something of a mystery, and there is as yet no generally accepted theory, although many people have very pronounced views on the subject. Many puzzling facts have been noted since investigating the disease in Pennsylvania, among them being the large percentage of infection in eastern York and southern Lancaster counties, the relative small percentage in certain localities around which the blight is generally prevalent, and recent infections found in Warren and other western counties, a great distance from what is known as the western advance line of the disease.
Our pathologists have reported some very interesting facts in regard to the dissemination of the blight. In the preliminary report of the summer's work at our field laboratories the results tend to show:
First, the prolific ascospore stage is very important in causing the spread of the blight, the spores at this stage being forcibly ejected from the pustules and borne through the air for some distance. This ejection of spores takes place under natural field conditions only when the bark has been soaked by rain, but the expulsion of spores is also dependent upon temperature conditions and ceases entirely at temperatures from 42 to 46 degrees F. and below.
Second, the wind plays a large part in local ascospore dissemination.
Third, birds and insects (except ants) are apparently of very little importance in the dissemination of the blight except in providing wounds. Further investigations of the importance of ants is being made during the present winter.
Several kinds of beetles have been observed eating the pustules and are in this way beneficial, since tests show that they digest and destroy the spores. It has also been suggested by workers in the Bureau of Entomology that such beetles, which are of several kinds, may be of value in the attempt to control the disease. These are perhaps the only natural enemies discovered to date.