Page:Popular Science Monthly Volume 84.djvu/558

554 and impressions of one and perhaps two species found in the miocene rocks of Oregon, and in those of the upper miocene of the Colorado parks, show that Castanca, which already existed in Europe in the cretaceous period, once inhabited western North America, whence it has now disappeared."

Coming now to the condition of the chestnut tree to-day, let us first figure up its liabilities, i. e., those diseases and injuries from which it is prone to suffer, and then set down on the other side of the balance sheet its assets, i. e., those inherent qualities which accrue to its advantage in the struggle for existent

It is a significant fact that both the European and the American chestnuts have been attacked in recent years by serious diseases which have attracted a great deal of attention here and abroad. In Europe the disease known as the Male dell' Inchiostro and various other troubles have very seriously affected the European chestnut.

In the United States, the well-known bark disease, discovered in 1904 near New York City, has already caused enormous damage to the chestnuts in southern New England, New York, New Jersey, Pennsylvania, Delaware and Maryland, and it also occurs in Virginia and West Virginia (Fig. 1). It is unnecessary here to describe this trouble in detail, as excellent accounts of it have already been published and are easily available. It is sufficient to state that it is caused by a fungus which grows in the living bark of the tree, gaining an entrance through wounds or openings of any sort in the bark. As the fungus grows, it kills the bark, and by gradually increasing the radius of its operations, eventually reaches around the trunk or branch which it entered, in this way girdling it.

When this disease was first discovered, and its disastrous nature realized, one of the first questions that are that of the source of the causal fungus. Where did this fungus come from? Was it a native fungus, or was it brought into this country from abroad? It was easily seen that the answer to this question was of fundamental importance, for if the fungus was a native species, then its sudden attack was evidently due to unusual environmental factors of some sort, and with the recurrence of the normal conditions the virulence of the attack would cease. On the other hand, if the fungus were an imported parasite, there would be no telling where its depredations would end.

Those who held to the first theory, i. e., that the fungus was a native