246 
masses. No difference in the varieties can now be seen, except that 
the Keiffer is a little behind. In two days longer mould set in and 
stopped the experiment. In generalizing from this it will not do to 
place much stress upon the action of the Keiffer pear, as the prob- 
ability is entirely in favor of the difference being accidental. 
The conclusion seems reasonable that so far as the green fruit is 
concerned, with an equal supply of sap in the different varieties 
there would be equally rapid and copious blighting. Upon this hy- 
pothesis the reason a Bartlett pear gives so much more pronounced 
results from artificial inoculation than a Seckel or Buffum is due to 
the larger per cent. of sap it contains. But we do not care to carry 
this argument far till the investigation 1s more complete. 
From the first announcement that bacteria were the cause of 
blight, it has been taught that in pruning away the diseased branches 
the knife should be constantly disinfected with carbolic acid or some- 
thing equally effective. All experience in artificial inoculation has 
shown that it is difficult to start the disease in any part of the tree 
except the young and succulent tissue at the growing ends of the 
branches or in the flowers and green fruit ; these are not the parts 
that are usually touched by the knife in pruning, and the precaution 
urged against spreading the disease with the knife seemed from this 
to be unnecessary. But there isno argument so good as a rigid dem- 
onstration, and hence the matter was subjected to experiment. A 
knife blade was thoroughly smeared with the exudation of a fully 
blighted Flemish Beauty pear and was then used to cut off a 
well ripened twig of this year’s growth from a Bartlett pear tree 
(Exper. 406); this was repeated on three other twigs of same tree 
(Exper. 407, 408, 409). ‘The trial was varied by cutting off half 
the length of vigorous sprouts which had started up from the 
base of two trees with a knife treated as before (Exper. 410, 
411, 412, 413). The knife was drawn several times through 
a freshly blighted branch of Bartlett pear, then used to cut 
off a branch of present year’s growth, fairly matured, on another 
Bartlett tree; repeatéd the operation (Exper. 414, 415). The next 
two experiments (416 and 417) were like the last but on a branch of 
last year’s growth. Of these twelve trials, done with far more 
thoroughness than is likely to occur in ordinary operations, only the 
last mentioned one conveyed the disease. The excisions were made 
on August 5th; an earlier date may have been more favorable to the 
disease, but on the other hand in practice the limbs are not likely 
to be cut so near the ends. There can be but one conclusion—that 
the danger of spreading the disease with the pruning knife is not 
great enough to warrant the extra trouble of keeping the blade dis- 
infected. 
A large number of experiments have been carried on in cultivat- 
ing the blight bacteria in various nutrient solutions, such as infu- 
sions of corn meal, starch, hay, cooked pear, sugar, barn-yard 
manure and nutrient gelatine, of which corn meal gave the best re- 
sults and sugar the poorest. In a day or two after introducing the 
least amount of virus into the culture liquid, say of corn meal, it 
became turbid with the great increase of the bacteria. In solid 
gelatine each bacterium formed a_ spherical colony which be- 
came large enough to be distinctly visible, but did not liquify the 


