New York AGRICULTURAL EXPERIMENT STATION. AST 
1. Because there was no other adequate source of infection in 
the vicinity. | 
2. Because the area under the drip of the branches of the 
Bavay’s Green Gage showed the disease in very great abundance, 
while outside this area only occasionally was a diseased nursery 
tree found. So marked was the areamof greatest amount of 
disease that the owner was decidedly of the opinion that the 
infection came by the absorption of a poison by the roots of the 
young trees from the roots of the old trees. 
The question as to how long a period of time may elapse after 
infection with the Black Knot spores before the appearance of 
conidia on the newly-formed knots may in this instance be 
answered quite definitely. The wood of\the stock on which the 
Gueii were budded was all cut away prior to the summer of 1892, 
therefore the infection, in the great majority of cases at least, 
could not have come through the previous infection of the stock, 
for the outbreak of the Black Knot in most instances was at too 
great a distance from the stock to admit of the possibility of 
infection by growth of mycelium from that source; moreover, in 
no instance was the Black Knot observed below the union of the 
bud and stock. The infection could not have come from the 
ascopores during the winter and spring of 1893, because the 
owner asserts that the knots on the Bavay’s Green Gage were 
cut away in the fall of 1892 and no old knots were noticed on 
these trees in June, 1893. 
Although not the result of a direct experiment, the conclusion 
seems irresistible that the infection came from conidia produced 
in the summer of 1892. The first outbreak of the disease on the 
Guell trees was observed June 18, 1893, when eleven fresh 
spongy knots were found. Had any outbreak occurred much 
previous to this time it could hardly have escaped the observa- 
tion of those who cultivated the trees. No outbreak of the dis- 
ease on the Gueli trees was observed during 1892, the season in 
which the infection took place. Within a few days after the first 
knots were seen on the Gueii, June 18, 1893, the disease appeared 
in great abundance in the infected areas. 
In this instance there seems to be no reason to doubt that trees 
which were infected with Plowrightia morbosa (Schw.), Sacc., 
