WORK OX TIIK W HITE PINE BLISTER RUST IX MIXNESOTA 



15 



dispersal are fountl in lairds, 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- 

 ([uarter inch across, and more or less 

 elliptical in shape, is accompanied by 

 a swollen, unnatural appearance of the 

 bark of the tree on the aiTected 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 l)y the wind and prob- 

 ably by some of the other agencies 

 mentioned above, infesting other 

 leaves upon 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 aljundant. During June and 

 Julv one finds present uredospores. 

 Late in July (July 22nd was our first date at Dry Creek) another stage 

 is found upon the leaves of alTected Ribcs. The spores in this latter 

 stage are present until Autumn, being known as "teliospores." These 

 cannot reinfect currants nr 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. Bureau of Plant In- 

 dustry, U. S. Dep. of Agr. 



