COMMUNICABILITY OF THE DISEASE. ul 
experiment and six years later, when the trees were dug, is given in 
Tables XXXIV and XXXV, in the appendix. 
The results from the experiments, as shown in Tables XX XIV and 
XXXV, are as follows: The orchards were planted with trees 50.1 
per cent of which were diseased with crown-gall. At the close of 
six years 40.5 per cent of the original number of trees was diseased, 
of which 15.8 per cent was diseased with crown-gall and 24.7 per 
cent with hairy-root. 
Of 416 trees alive at the end of six years, 226, or 54.3 per cent, 
were healthy, as compared with 49.9 per cent of the original number. 
In order to further analyze the results of the experiment, Tables 
XXXVI and XXXVII are given, with the separate record of the 
healthy and diseased trees in each plat. 
From these tables it will be seen that, after deducting the dead 
trees, 1 out of the 83 healthy ones in orchard 1 had become diseased 
with crown-gall and 18 with hairy-root; and out of the 70 healthy 
trees in orchard 2, 10 had become diseased with crown-gall and 29 
with hairy-root; but it was noted at the time of digging that in 
every case the amount of disease on the newly infected trees was 
slight, the badly diseased trees in the plat after six years being 
few in number and among those that were originally diseased. In 
comparison with this increase of disease it must be noted that, after 
deducting the number of dead trees, out of 96 diseased trees planted 
in orchard 1, 32 fully recovered and out of 139 diseased trees planted 
in orchard 2, 41 recovered entirely. In other words, where 58 trees 
became slightly diseased, 11 with crown-gall and 47 with hairy-root, 
73 trees recovered from crown-gall during the same period without 
any treatment whatever. 
This slight communicability shown by traces of disease is cer- 
tainly almost negligible from the standpoint of the orchardist and 
must have occurred during the first growing season, since great care 
was taken not to wound the trees by cultivation. The experiment 
certainly indicates that apple trees when they are once established 
are not in danger of becoming seriously diseased on the roots if 
cultivated carefully and without imcurring wounds, even when 
every tree 9 feet away in the adjacent rows is diseased, as in the 
experiment. There appears, then, no need of removing diseased 
trees from orchards, except when they are not doing well; that is, 
when they show every indication of becoming unprofitable or when 
there is danger of communicating the disease to valuable small fruits. 
The matter of communicability as it applies to other apple trees in 
the orchard need hardly he considered when the question of removal 
is being taken into account. 
186 
