In the first place in every disease problem, conspicuously so with our fruit and nut diseases, there are two main classes of plants to be considered, our native plants and the foreign plants. The pathologist is always looking to the native origin of a plant in studying its adaptation to the environment in which it is attempted to be grown. A foreign plant may not necessarily be unadapted to another locality. The vinifera grape is thoroughly adapted to California and to much of the Pacific slope beyond the Rocky Mountains, but you know the vinifera grape has a hard struggle in other parts of the United States. This is not only a pathological problem but a physiological one. It cannot stand a soaking rain for two weeks at a time; it cannot stand so much water and humidity but it wants dry, hot sunshine continuously from the time it puts out its leaves in the spring. Another phase still more interesting is the question of foreign parasites. Many of the worst diseases with which we have to contend are either native diseases attacking introduced plants, or foreign diseases attacking native plants. I will take that up in detail. Nature has fought the battle all out with the native parasites against the native host plants, so we don't have to do it. It's a case of the survival of the fittest. They have won, so when we are dealing with native plants against our native diseases, we have a condition that has been fought out in nature for nobody knows how many thousand years. The result is that unless we disturb the balance too much by cultivating great orchards of a thing that has been grown as scattered individuals, or overforcing it or selecting and breeding towards larger fruit without any regard to foliage and other characters we can go ahead with our breeding and selection and cultivation and trust nature to keep the balance to some extent. We have this natural balance in our favor in dealing with the problem of cultivating native plants. As an example take the pear and apple blight. The pear blight problem is one in which a native parasite on wild crab apples, which occasionally kills a few twigs here and there, attacks the juicy, tender, susceptible, introduced European pear and makes a very serious disease. It is a fight indeed to grow it in so much of the country that pear culture has been very largely suppressed over the eastern half of the United States and part of the Pacific coast. All this trouble has been caused by one little native microbe. Apple culture also, with certain varieties, has been seriously interfered with in some sections.