54 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
digging every third tree; one-half of the remainder, or each alternate 
tree, were dug at the end of the second year, and the remaining trees 
were dug the third year. The combined results from these experi- 
ments are given in Table XXXI, in the appendix. 
In experimental set 2 the conditions in set 1 were duplicated and 
the grafts planted in cooperative plat 6 in 1905. One-third of the 
trees, as before, were dug at the end of the first year, but at the end 
of the second year it became necessary to dig the remainder on 
account of the more rapid growth of the trees in this locality. The 
results from this experiment are given in Table XXXII. 
In experimental set 3 the conditions of set 1 were duplicated and 
the grafts planted in cooperative plat 5 in 1905. One-half of the 
trees, selecting each alternate tree in the row, were dug at the age of 
2 years and the remainder at the age of 3 years. The results from 
this experiment are given in Table XXXITTI. 
The results from the three sets of experiments are summarized as 
follows: 
(1) They show a decrease of crown-gall in trees in nursery rows 
after the first year; in set 1 a decrease from 26.7 per cent the first 
year to 9.1 per cent the second and to 4.7 per cent the third; in set 2 
from 20 per cent the first year to 12.8 per cent the second; in set 3 
from 11.7 per cent the second year to 2.6 per cent the third. 
(2) They show a general and decided increase of hairy-root the 
second year, with a slight or no increase the third. In set 1 there 
Was an increase from 5.5 per cent the first year to 8.6 per cent the 
second and 8.7 per cent the third; in set 2 from 7.9 per cent the 
first year to 10.3 per cent the second; in set 3 from 6.4 per cent the 
second to 10.2 per cent the third year. 
(3) The increase in hairy-root does not nearly offset the decrease 
in crown-gall and some of the trees must throw off the disease and 
recover. In set 1 crown-gall decreased 22 per cent, while hairy-root 
increased but 3.2 per cent. In other words, the number of diseased 
trees decreased 18.8 per cent. In set 2 crown-gall decreased 7.2 
per cent, while hairy-root increased 2.4 per cent, and of diseased trees 
there was 3.8 per cent less. Im set 2 the percentage of crown-gall 
decreased 9.1, while that of hairy root increased 3.8, and of diseased 
trees there was a decrease of 5.3 per cent. 
In conclusion, the time when the disease is communicated to the 
trees is during the first year. In the light of experiments already 
described the communicable period must be during the time of the 
formation of callus for closing the wounds in the union of scion and 
root. 
These experiments show that crown-gall as a rule does not spread 
from tree to tree in the nursery after the first year and that hairy-root 
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