14 FARMERS' BULLETIN 742. 



unlike the uredospores, can not repeat their development upon the cur- 

 rant leaves, but in order to carry on the disease they must attack the 

 bark of young white pines or of young parts of old white pines (fig. 4, 

 d and a). The teliospores, falling upon bark of suitable age on a white 

 pine, may in turn germinate, penetrate the bark, and grow in the 

 inner layers during the incubation period already mentioned. This 

 infection of the pine bark must take place in the late summer or fall. 

 If the parasite finds conditions very favorable, it may produce the 

 sweetish drops of liquid with the pycnospores early the next spring, 

 and shortly after that it may produce the blisters containing the 

 Peridermium spores. The Peridermium stage is visible on the pines 

 from the latter part of April until the middle of June. This com- 

 pletes the life cycle of the parasite. Because of the fact that the 

 Peridermium spores produced upon pine can not infect pine and 

 that the teliospores produced upon currants can not infect currants, 

 we immediately perceive that if the two sets of host plants are 

 separated widely enough so that the spores produced upon one can 

 not reach the other the disease can not spread. 



EFFORTS ALREADY MADE TO CONTROL THE WHITE-PINE BLISTER 



RUST. 



In Europe this disease was firmly established before any eradica- 

 tion of plant diseases was attempted, and the only effort there 

 exerted is merely to keep it in check. There has never been, pre- 

 viously, either in Europe or America, any serious attempt to eradi- 

 cate a disease of trees of this type; that is, we have had no earlier 

 experience with a disease of this sort by which to guide our attempts 

 at controlling this one. It was in 1909 believed feasible to remove 

 all of the diseased trees from an infected lot of pines during the 

 course of two or three years by repeated annual inspections in the 

 spring when the fruiting bodies of the parasite are most conspicuous 

 on pines. The work then attempted was done with this end in 

 view. It has become increasingly evident since that time that such 

 annual inspections would have to be repeated for an indefinite period, 

 as it has been found that the parasite apparently may lie dormant 

 in an infected tree for six or more years before becoming externally 

 visible. This means that inspection is not efficient. The alter- 

 native seems to be that of the total destruction of the entire lot of 

 pines known to be infected. In the work done up to the present 

 time, special emphasis has been given to the removal of all wild and 

 cultivated currants and gooseberries from dangerous proximity to lots 

 of pines known to be infected with the white-pine blister rust. 



It has been found, however, in these investigations that the 

 various State officials, who necessarily must perform this work, do 

 not have power to destroy such currants and gooseberries as may 



