8 
WORK ON THE WHITE J>1NE r,LlSTl-:R ROST IN MINNESOTA 
dispersal are found in birds, various insects, cattle and other quadru- 
peds, as well as man himself. 
During May (perhaps also in April ) June and early July in Min- 
nesota open and closed blisters may be seen on twigs or large branches 
or even on trunks of five-leaf pines. 
The presence of these blisters, white 
just before opening and about one- 
quarter inch across, and more or less 
elliptical in shape, is accompanied by 
a swollen, unnatural appearance of the 
bark of the tree on the affected por- 
tion. Blisters, which have opened, dis- 
close the yellowish or orange spores 
( peridermium spores ) within. These 
after a few weeks are disseminated, 
those reaching the leaves of currants 
and gooseberries starting upon the un- 
der side of the leaves, if the weather 
is not too dry the second stage in the 
life history of the fungus, attacking 
the leaves by sending tiny root-like 
processes into the living tissue and 
later developing very small yellow 
masses of spores on the under side. 
These spores are called uredospores : 
they are spread by the wind and prob- 
ably by some of the other agencies 
mentioned above, infesting other 
leaves iqion the same bush or upon 
other bushes. This form of reproduc- 
tion continues during a large part of 
the summer, and in this way the dis- 
ease may spread long distances if cur- 
rants or gooseberries, wild or culti- 
vated, are abundant. During June and 
July one finds present uredospores. 
Late in july ( fulv 22nd was our first date at Dry Creek) another stage 
is found upon the leaves of affected Ribcs. 1 he spores in this latter 
stage are present until Autumn, being known as “teliospores. These 
cannot reinfect currants or gooseberries, but must go to the bark of 
pines in order to continue the life of the parasite. As before stated, the 
disease mav remain dormant, or at least not visible on pine for from 
Fig. 2. Young white pine showing 
swelling and pycnidial drops 
of liquid caused by blister 
rust. Ilureau of Plant In- 
dustry, U. S. Dep. of Agr. 
