279 
The disease in other than pear trees.—It is generally 
recognized that the disease is most strongly manifested in 
the pear and cultivated crab-apple ; in the common apple 
or i andthe quince it is less destruc- 
Se 
Aye: 




Mate =! : on Fates ane sed z 3 i 
TNE See = sttive; it has been established, 
oot, ee SO He tly t a t and t 
a ea ai EN partly by experiment and part- 
ae akceeat ~ f- S\ ¥ly by observation, that, in a less 
th Le, ‘ A ed Veg a ; 
Air, Wing Yo as 2 ts > g i legree, it also affects the moun- 
“RS oD ee #:cain ash, service-berry, English 
“te, ie ee” hawthorn and other thorns. 
Nee rey gg TET 
| Bl eile During the last season this list 
Fig. 4,—Part of LOZ ova mass has been extended by the suc- 
showing an envelope free from cegsful inoculation of the fruit 
eng Magnified 890 diam- 4nd branches of the wild crab- 
apple, Pirus coronaria, in which 
the disease took as readily and progressed as rapidly as in 
the common apple. It would be interesting to know if, 
during a season of epidemic, the wild crab-apple is not at- 
tacked by the disease like the common apple. . 
Several writers have expressed the belief that the same 
disease affects a number of other designated trees and 
shrubs, not belonging to the pome family. Some of these 
suggestions have been acted upon, and their trustworthiness 
put to the test, by a series of inoculations with the blight 
virus. 
On June 8 three succulent shoots of an elderberry (Sam- 
bucus Canadensis) were inoculated with fresh virus washed 
from blighting pear twigs, and at the same time the same 
virus was used to inoculate the young shoots and fruits of 
quince, and the fruits of Bartlett and Seckel pears. The 
pear and quince inoculations set up the disease, but no more 
effect was produced on the elderberry than if pure water 
had been used instead of blight germs. The experiment 
was repeated on June 18 with uniform results. In no res- 
pect could the conditions be more favorable for conveying 
the disease than were secured in these triais, and the abso- 
lute failure of the elderberry to be infected must be consid- 
ered ample proof that it is not a susceptible plant. 
On June 10 succulent and vigorous shoots of Abele poplar 
(Populus alba) and of balm-of-Gilead (Populus balsamifera. 
var.) were inoculated in the usual way. In each instance the 
wounds healed the same as if no virus had been applied. 
The experiments of each succeeding season make the 
conviction stronger that only pomaceous species are suscep- 
tible to this disease. : 
Internal conditions affecting the disease.—The factors 
which modify the growth and activity of the germs within 
the plant yet remain comparatively obscure. Why one 
species of bacteria will thrive in the living tissues of a pear 
19 
