Apr. 1, 1925 
Relation of Weather to White Pine Blister Rust 
597 
sive years, it is practically certain that 
infection resulted from exposure to 
sporidia in the last of these years. 
A great many of the cankers found 
in 1922 had evidently produced aecia 
for three years, apparently beginning 
in 1920. This would indicate infec¬ 
tion in 1917. Tabulations made in 
1922 included all the infections found 
in any one place regardless of their 
stage of development. Table VI shows 
the distribution of 110 cankers found 
July 18, 1922, in one limited area near 
Mile 72, Pacific Great Eastern Rail¬ 
way, British Columbia. 
Table VI.— Distribution of 110 cankers 
found July 18, 1922, near Mile 72, 
Pacific Great Eastern Railway, British 
Columbia 
Internode of— 
Number 
of infec¬ 
tions 
1914_ 
1 
1915_ 
8 
1916_ 
59 
1917_ 
42 
The data in this table are fairly 
typical for the distribution of the 
older cankers which were found in 
many places. Infection in 1917 is 
indicated. 
Table VII shows the distribution of 
54 cankers as found by A. T. Davidson 
( 1 ) May, 1922, in a swamp at North 
Vancouver, British Columbia. 
Table VII.— Distribution of 54 cankers 
found May, 1922, in a swamp at 
North Vancouver, B. C. 
Internode of— 
Number 
of infec¬ 
tions 
1912 or 1913__ 
5 
1915...__ 
8 
1916_ 
29 
1917____ 
12 
With the exception of the five in the 
internodes of 1912 or 1913, these 
cankers were apparently of the same 
stage of development. They were 
probably the result of infection in 
1917. The five in the internodes of 
1912 or 1913 were several years older 
than the others. Some of them had 
started in branches which were dead 
when found in 1922. It was impossible 
to determine within two or three years 
the internode in which infection first 
occurred. A reexamination of one of 
the old cankers showed that it might 
have had its origin in the internode 
of either 1910 or 1911. 
A few of the oldest cankers were 
found in other places. Two at Daisy 
Lake and one at Mile 28, Pacific 
Great Eastern Railway, evidently 
started in the internodes of 1912 or 
1913. One at Thurston Bay, British 
Columbia, appeared to have started 
in the 1912 internode; one on Green 
Mountain, a mile from Bold Point, 
might have started in either the 1910 
or the 1911 internode. 
These oldest cankers were not less 
than 3 nor more than 5 years older 
than the cankers which seemed to 
have resulted from infection in 1917. 
All of them had their origin in the 
internodes of the years 1910 to 1913, 
inclusive. Although it is not certain 
that all began in 1913, any or all of 
them, from their apparent stage of de¬ 
velopment and position, might have 
resulted from infection in 1913. Tab¬ 
ulations of cankers in the immediate 
vicinity of these oldest cankers do not 
indicate infection in 1914 or 1915. 
They do indicate, however, that there 
was a little infection in 1916, much in 
1917, a little in 1918 and 1919, much in 
1920, and a great deal in 1921. If the 
oldest cankers had resulted from infec¬ 
tion before 1913, there should have 
been enough aeciospore production to 
have caused at least a little infection 
of Ribes and pine in the immediate 
vicinity earlier than 1916. 
The data presented might seem to 
indicate that pine infection in any 
given locality has been largely propor¬ 
tional to the number of aeciospores 
produced in that locality. This is un¬ 
doubtedly true in limited areas where 
an abundance of Ribes is present. It 
is also true that the greater the amount 
of aeciospore production the greater 
the chances for their wide distribution 
and infection of Ribes. The more 
important fact, however, is that initial 
infection of pine in localities where the 
disease has not previously occurred, 
and heavy infection near Ribes as well 
as at some distance from them, have 
not been proportional to aeciospore 
production. From the data obtained 
it is evident that the rust became es¬ 
tablished in several localities, probably 
in 1913. No evidence was found to 
indicate that it was established in any 
other locality before 1917. There is 
no reason to believe that there were 
less aeciospores in 1914, 1915, or 1916 
than there were before 1914. As a 
matter of fact, there were probably 
many more in 1916 than in any pre¬ 
vious year. 
