Mr. Reed: From the chart, it appears that the disease is more common in the vicinity of streams and bodies of water.
Professor Reddick: That is an observation that has often been recorded.
Mr. Reed: How is it elsewhere than in New York?
Professor Collins? The question has been asked more often than otherwise, why do we find the disease on the tops of hills away from the water? I think there isn't a sufficient amount of evidence or observation on that point to say whether it is more common near or away from bodies of water.
I will call your attention to one experiment that can be performed by anybody with the microscope. Take a piece of one of those spore horns or threads, put it in a drop of water on a microscope slide. Inside of two minutes, it will disappear entirely. It is dissipated in the water, and the spores are so small you cannot see them with the naked eye. If you let the water dry on the slide, then put that slide under the microscope and try to blow those spores off, you can do it just about as easily as you can blow the shellac off a door. You can brush that film under the microscope, and you can't see that a single spore has been disturbed. The explanation, I think, lies in the fact that these spores are of a mucilaginous nature, and when they dry, they stick to whatever they come in contact with. That does not mean that these spores cannot be blown, because they may lie on fragments of leaves and be blown about by the wind. Again, some of the spores may be detached in a mechanical way and thus blown by the wind. But I am quite convinced that the spores are not blown broadcast, simply because they are of a sticky nature.
Now, those spore threads are forced out under certain conditions, moisture conditions, as a rule. It has been shown after repeated observation that these spore threads are pushed out a day or two after a rain. Of course, in the springtime, the atmosphere is much more moist than later in the season. Consequently, we find more of these spore threads in the spring than at any other time. You will recall that the last week of August this year was a week of almost continuous rain. Two days after that ceased, I saw as many of these spore threads as I had seen at any one time all summer. So that, although conditions are best in the spring for greater abundance of these spores, they may occur at any time. If a bird alights on these spore masses, there is no reason that I see why they should not be carried. We know the rain water running down the trunk dissolves these spore masses, and they are carried down, there to reinfect the tree when insects crawl around.
President Morris: My brother has some Japanese chestnuts twenty-five or thirty years of age. By cutting off one branch at a time as fast as they blighted, he has saved those trees.
Professor Collins: You spoke, Doctor Morris, of grafting Japanese on to American stock. I have seen repeated cases where the Japanese has been grafted on to American stock. The whole Japanese tree has been killed, and we find the disease has killed the tree by girdling the American stock below the graft.
President Morris: Yes, I find this over and over again. In one case where I had a very choice variety of Burley's chestnut, the Diaporthe attacked the American stock underneath this, and had practically girdled it when I saw it. There remained a fraction of an inch of good bark. I cut off all except that, and put tar over it, and grafting wax over that, and this year the graft has grown a foot or more. So by giving a great deal of attention to some one little injury, we can overcome the effect of it.
Mr. Jensen: In your grafting, what was the relationship of the rapidity of the growth of top after grafting, compared with the old stock?