28 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE: 
in different valleys. The trees from the two sets of grafts made from 
these seedlings, however, were grown under similar conditions, and 
the results of the experiment are of value, since they show what 
variation may be expected from seedlings grown in different locali- 
ties and since they disprove the prevalent idea that Kansas seedlings 
are more apt to develop crown-gall than others. The results show 
a decrease of 3.4 per cent in crown-gall and of 1.1 per cent in hairy- 
root on trees from grafts on Kansas seedling roots. This is almost 
entirely offset by the increased stand of trees, 3.1 per cent, obtained 
from the trees grown from grafts on Nebraska seedling roots. The 
experiment, then, yields no positive proof of an increase of the dis- 
ease where seedlings are purchased from localities where nursery 
stock has been grown for years. 
Heavy wet soils favor the development of crown-gall in the nursery.— 
The consensus of opinion of nurserymen, based upon observation, has 
been that heavy wet soils underlaid with or composed largely of clay 
favor the development of crown-gall. No extensive set of experi- 
ments on this subject has been recorded. The most extensive experi- 
ment recorded in scientific publications is that of Howard regarding 
the increase of crown-gall due to clayey soil as compared with loess. 
A large number of experiments have been conducted by the writer 
on different kinds of soils, only two sets of which were conducted 
in the same locality. These were on cooperative plats 1 and 2. 
Plat 1 consisted of a low wet tract of land, composed of a colluvial 
clay loam laid to a depth of 3 to 4 feet on a stratum of yellow clay. 
Plat 2 was an upland, well-drained, light clay loam of about equal 
depth, sloping gently to the south. The two plats were planted with 
an equal number of root grafts made from healthy stock and prepared 
in equal lots from twenty-four varieties of apples. The names of these 
varieties are given on page 85. One-third of the trees, selected in a 
numerical series, were dug each year for three successive years, at 
the ages of 1, 2, and 3 years. The results are given in Table XII, in 
the appendix. 
Nearly the same amount of disease occurred in the two plats, 24.9 
per cent in plat 1 and 24.1 in plat 2. There was a preponderance of 
5.3 per cent of crown-gall on the heavier, wetter soil, and 4.5 per cent 
of hairy-root on the higher, drier soil. Without regard to the cause 
of the different forms of the disease, the usual rule with regard to the 
increased production of roots in drier soils holds good in these experi- 
ments. The well-drained upland soil in plat 2 yielded 20.2 per cent 
more good trees than the other plat. These, however, were at least 
a third smaller in size. 
Six other cooperative plats, 3 to 8, were planted with experiments 
identical with those in plats 1 and 2, since the root grafts for each 
186 
