38 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
It was planted with the same varieties, but the healthy trees, 122 
in number, were planted in blocks of several rows, rows of healthy 
trees alternating with rows consisting of 139 diseased trees. Both 
orchards were cultivated across rows, from diseased to healthy trees, 
to facilitate the spread of disease by cultivation. One block of 36 
diseased trees of the Collins variety in this orchard was composed of 
trees diseased with the soft form of crown-gall, the other varieties 
being diseased with the hard form. Most of the galls were from 14 
to 2 inches in diameter. 
Orchards 1 and 2 were cultivated with ordinary care, receiving 
no special attention. The trees were planted thickly and stood 8 
by 9 feet apart. The soil was not the best, owing to the fact 
that it had been cultivated to grain crops without fertilization for 
many years. No fertilizer was used, natural soil conditions being 
preferred. The growth of the healthy and the diseased rows was so 
nearly uniform that on repeated tests trained pathologists could 
not pick out the rows of diseased trees. Photographs of represen- 
tative rows of trees were taken at the age of 6 years (see Pl. X). 
Owing to a fire which killed many of the trees in orchards 1 and rl 
the experiments had to be discontinued, and the trees were taken up 
when they were 8 years old; that is, after they had grown for six 
seasons in the orchards. Just before the trees were taken out, the 
trunk of each was carefully measured at a height of 6 inches above 
the surface of the ground. At the time of removal careful notes 
were taken of the condition of the roots as to increase of disease, 
recovery therefrom, forms of disease, etc. The results of the experi- 
ment are given in a condensed form on pages 20 and 57 and in Tables 
XVII, XVIII, and XIX, in the appendix. Table XVII gives the 
average diameter of the healthy and the diseased trees at the time 
they were dug. 
Tt will be seen from Table XVII that the effect of crown-gall and 
hairy-root on the trees in the experiment was to diminish Very slightly 
the diameter of the trunks. The trees with healthy roots had 
developed in six years an increase in diameter of six one-hundredths 
of an inch greater than those diseased with hairy-root, and of twenty- 
nine one-hundredths of an inch greater than those diseased with 
crown-gall. These diseases are thus shown to be very slightly 
detrimental to the growth of orchard trees during the first few years, 
and the assertions of many to the contrary are disproved. 
In orchards 1 and 2, during the six seasons of growth the number 
of healthy trees that died was 23 out of 234, or 9.8 per cent, and of 
diseased trees 1t was 30 out of 235, or 12.8 per cent, indicating that 
the presence of the disease may have slightly increased the death 
rate. During the first four years 9 healthy and 9 diseased trees died. 
186 
