Inoculations
The very fact that these trees are now alive in this New York region is pretty good proof of their resistance. But of course the most conclusive test is by inoculation with the fungus in question. If the fungus grows slowly in these trees as compared with its growth on non-resistant stock, then no one can deny that they are resistant. I will not bore you with figures of tables, I will only give you the results. The average growth of the fungus in 289 inoculations on the resistant trees was about ⅓ as fast as on non-resistant stock, and taking the rate of growth on those trees which are especially resistant it is about ¼ as fast as on the non-resistant stock. For non-resistant stock the seedlings on Staten Island were inoculated, and the growth on these tallied very closely with growth in non-resistant trees inoculated by Anderson and Rankin.[3]
Another very striking result brought out by the inoculation work was that of the 158 inoculations on branches and basal shoots of the resistant trees, only nine had been girdled after one month's growth, while in the same time 16 out of the 32 non-resistant Staten Island trees were girdled. At the end of the second month, the results were still more striking. Then, in the Staten Island trees, 22 out of 32 were girdled, while in the inoculations on the basal shoots and branches of resistant stock only 22 out of the 153 resulted in girdling. This striking difference was not due to smaller diameters of the Staten Island trees, for particular pains were taken to have them approximately equal to the branches and shoots inoculated in the resistant trees.