604 
Journal of Agricultural Research 
Vol. XXX, No. 7 
Table XVI.— Precipitation, in inches, 
during June, July, and August, 1871 
to 1922, inclusive, at Summit, Calif. 
June 
July 
August 
Total 
1871.. 
0.89 
0.00 
0.00 
0.89 
1872_ 
.00 
.00 
.00 
.00 
1873... 
.00 
.03 
Trace 
.03 
1874_ 
Trace 
.00 
.00 
1875_ 
2. 55 
Trace 
.00 
2.55 
1876_ 
Trace 
1. 21 
.10 
1.31 
1877_ 
.12 
.00 
.00 
.12 
1878_ 
.00 
.00 
.09 
.09 
1879_ 
.10 
.00 
.00 
.10 
1880.. 
.00 
.80 
.00 
.80 
1881_ 
.50 
.00 
.00 
.50 
1882_ 
.00 
.00 
.00 
00 
1883... 
.00 
.00 
.00 
.00 
1884_ 
4.04 
.00 
.00 
4.04 
1885_ 
.80 
.00 
Trace 
.80 
1886_ 
.00 
.00 
.00 
.00 
1887..... 
1.60 
.10 
Trace 
1. 70 
1888...... 
3. 72 
3. 51 
.28 
7. 51 
1889__ 
.22 
.00 
.00 
.22 
1890__ 
.00 
.00 
.00 
.00 
1891_ 
.00 
.00 
.00 
.00 
1892. 
.20 
.00 
.00 
.20 
1893_ 
.00 
.00 
.00 
.00 
1894__ 
.00 
.00 
.00 
.00 
1895__ 
.00 
.00 
.00 
.00 
1896..... 
.00 
.21 
.02 
.23 
1897__ 
0. 70 
0.00 
0.00 
0.70 
1898_ 
.90 
.00 
.00 
.90 
1899.. 
.70 
.00 
1.00 
1.70 
1900..... 
.50 
.25 
Trace 
.75 
1901_ 
.00 
.00 
.00 
.00 
1902_ 
.30 
.00 
1.00 
1. 30 
1903_ 
Trace 
.00 
.00 
1904_ 
.05 
.04 
.03 
.12 
1905_ 
1.40 
Trace 
.00 
1.40 
1906_ 
2.10 
Trace 
1.00 
3.10 
1907_ 
2.22 
.12 
Trace 
2. 34 
1908_ 
.44 
.00 
.76 
1.20 
1909..__ 
.88 
.00 
.00 
.88 
1910_ 
.00 
1.16 
.00 
1.16 
1911_ 
.04 
.00 
.00 
.04 
1912_ 
.20 
.30 
.00 
.50 
1913_ 
.05 
2.45 
.15 
2.65 
1914_ 
1.19 
.00 
Trace 
1.19 
1915_ 
.00 
.55 
Trace 
.55 
1916_ 
.05 
.50 
Trace 
.55 
1917_ 
.00 
.00 
.21 
.21 
1918.. 
. 15 
.00 
.16 
.31 
1919_ 
.00 
.00 
.00 
.00 
1920__ 
1.60 
.00 
.67 
2.27 
1921.. 
.57 
.00 
.00 
.57 
1922.. 
.78 
.00 
.00 
.78 
DISCUSSION 
The prevailing winds and the distri¬ 
bution of precipitation through the 
summer months have favored the 
spread of the white pine blister rust in 
the coast region of British Columbia to 
the north and northwest, as well as 
along the valleys to the north and east 
through the Cascade Mountains. Al¬ 
though aeciospores have been produced 
in increasing numbers since 1913, at 
least, and there have been winds 
sufficient to carry them long distances 
in every direction, it is apparent that 
but one season in four has been favora¬ 
ble for any considerable spread of the 
rust. There was a little infection in 
the other years. This occurred, how¬ 
ever, only in the immediate vicinity of 
Ribes growing near pines with fruiting 
cankers. 
It is not difficult to understand why 
very little infection occurred in the 
years with light summer precipitation, 
as 1915, with a total of 2.18 inches and 
1919 with 2.28 inches, as compared with 
the average of 5.64 inches, and 6.81 
inches for 1917 or 6.80 inches for 1921. 
On the other hand, it is not easy to see 
why infection was not greater in other 
years with a fairly high summer pre¬ 
cipitation. In this connection it is 
necessary to note the requirements for 
general or heavy infection. 
Heavy precipitation in the period of 
aeciospore production has been ob¬ 
served to reduce greatly the dispersal 
of spores by washing them out of the 
aecia. In moist weather many of the 
aeciospores germinate within the aecia. 
Their germ tubes then prevent or 
retard the dispersal of the remaining 
spores. 11 After the spores are deposited 
upon Ribes leaves there must be a 
period with sufficient moisture to permit 
them to germinate and invade the leaf 
tissue. After uredospores begin to 
form there must be occasional moist 
periods to permit further infection of 
the leaves if there are to be any con¬ 
siderable number of telia produced. 
After telia are produced there must be 
a period favorable for the production of 
sporidia and the immediate infection of 
pine needles. 
The production of sporidia and the 
infection of the pine needle seems to be 
a most critical point in the life history 
of the rust. York and Snell (10) found 
that a continuous period of 18J^ hours 
with a practically saturated atmosphere 
is necessary to secure infection of the 
pine needle. The sporidia are delicate 
and short-lived. Whatever the combi¬ 
nation of circumstances or causes may 
be, it seems to be a fact that little 
infection of pine will result in the year 
with a very dry summer. It is also 
true that heavy infection does not 
always occur in years with normal or 
more than the normal summer pre¬ 
cipitation. 
The infection in the interior of 
British Columbia at Canoe, Revelstoke, 
and Beaton can scarcely be attributed 
to any other source than wind-borne 
aeciospores from the coast. The in¬ 
fection at Nakusp may have resulted 
in the same way or by aeciospores 
carried down the Columbia Valley 
11 From the author’s unpublished manuscript. 
