596 
Journal o f Agricultural Research 
Vol. XXX, No. 7 
aecia in 1920, 1921, or 1922. On the 
other hand, if the infections had oc¬ 
curred in 1921, there should have been 
some fruiting cankers in the 1921 
internodes. Several thousand infected 
branches and stems were examined in 
1923. In only one instance was a 
fruiting canker found in a 1921 inter- 
node. It is believed that aecia are 
usually produced in the third year after 
infection occurs ( 8, p. 25-26). 3 This 
is borne out by the writer’s field studies 
both in New York and in the North¬ 
west. 
From Table I it is evident that con¬ 
siderable infection occurred in 1920 
near Bold Point, British Columbia. 
Similar observations were made in 
other localities in the immediate vicin¬ 
ity of older pine infections and Ribes. 
As field observations were continued 
through the summer of 1923, it became 
increasingly apparent that there had 
been a great deal more infection in 
1921 than in 1920. The data given in 
Table II are typical for conditions 
found early in July with respect to 
incipient infections and those which 
produced aecia in 1923 for the first 
time. 
Table II.— Distribution of 141 infec¬ 
tions found early in July, 1923 
Internode of— 
Number 
of infec¬ 
tions 
1918_ 
13 
1919__ 
45 
1920 ... . _ .. ... . 
72 
1921_ 
11 
Nineteen of these produced aecia in 
1923 and were probably all infections 
of 1920. They were distributed as 
shown in Table III. 
Table III.— Distribution of 19 infec¬ 
tions, probably of 1920, producing 
aecia for the first time in 1923 
Internode of— 
Number 
of infec¬ 
tions 
1918. 
1919. 
1920. 
6 
11 
2 
The 19 infections shown in Table 
III subtracted from the 141 in Table 
II leave 122, distributed as shown in 
Table IV. These are all, or nearly all, 
infections of 1921. 
Table IV.— Distribution of 122 infec¬ 
tions found in July, 1923, all, or 
nearly all, of which are infections of 
1921 
Internode of— 
Number 
of infec¬ 
tions 
1918_ 
7 
1919_ 
34 
1920_ 
70 
1921 . 
11 
The totals 19 and 122 (Tables III 
and IV) show fairly well the relative 
number of 1920 and 1921 infections 
apparent by the first week in July. 
As the season advanced both the actual 
and the relative number of incipient 
(1921) infections increased. Table V 
shows the distribution of 162 incipient 
infections counted the second week in 
August. 
Table V.— Distribution of 162 incipient 
infections found during second week of 
August, 1923 
Internode of— 
Number 
of infec¬ 
tions 
1918_ 
2 
1919_ 
32 
1920.. _ . .. ... .. 
97 
1921_ 
31 
These tables indicate that in any one 
year infection may occur in the inter¬ 
nodes of four successive years. 
The western white pine commonly 
retains its needles four years; that is, 
during the summer of a given year, as 
1921, there will be needles upon the 
internodes of 1918, 1919, 1920, and 
1921. In a favorable season it is prob¬ 
able that infection may occur in any of 
these needles. Practically all the rust 
mycelium, however, which might de¬ 
velop in the oldest needles would fail to 
reach the bark, since those needles 
would die and fall by the end of that 
season. 
Since in any one year infection may 
occur in the internodes of three and 
occasionally four years, it is obviously 
impossible to determine by the position 
of a single canker the exact year in 
which infection occurred. When, how¬ 
ever, a large number of cankers of ap¬ 
proximately the same stages of devel¬ 
opment are found distributed through 
the internodes of three or four succes- 
3 Reference is made by number (italic) to “Literature cited,” p. 608. 
