The apple cedar rust is probably the most striking example of a native parasite attacking a foreign host that we know of, and particularly so as the remarkable evolution in which the parasite has adjusted itself to the new host is taking place right now every year. The apple cedar rust is becoming a more difficult problem clear across the eastern United States to Nebraska. It has occurred as a serious disease since 1905 to 1907. As a botanical curiosity we have known it a long time, but as a serious disease, it is very recent, and nobody knows yet how serious it is going to be. We have a very striking example of this introduction of a foreign plant and the plant being attacked by a native parasite, in the case of the filbert blight, and I am going to take that up later. The trouble is that we have brought into the United States a European filbert and it has been attacked by a parasite of our wild hazelnuts. The disease is very rare and is seldom seen on the wild hazelnut,--so rare that it was hardly known by scientific botanists, and yet it interferes with filbert culture in the eastern United States and is the one thing more than anything else to make filbert culture unprofitable. We have practically the same proposition in the walnut bacteriosis, not only in the northeastern United States, but in the best walnut districts of California. This bacterial disease which is undoubtedly a disease of our native walnuts--probably the native black walnut--occurs rather rarely, and so feebly developed as to be difficult to find at all on its native host yet it becomes the great serious disease of the Old World cultivated walnut.