REPORT OF THE SOCIETY 67 



the branch or stem year by year. Each spring there arise from the 

 swollen discolored tissue invaded during the previous year numerous pale 

 orange or whitish blisters filled with countless spores. It may take a 

 branch infection on a large tree a long time to kill the tree, but on the 

 other hand seedlings are killed very quickly, and as seedling trees are 

 more susceptible to attack, it may be seen that in or near an affected grove 

 the seedlings on which future forests depend would have little chance 

 of surviving. 



Like many other rusts this fungus passes part of its life on another 

 host— the Currant, or to speak more correctly, on all species of the genus 

 Ribes. Of these species, which include all the wild and cultivated currants 

 and gooseberries, the common garden black currant is by far the most 

 susceptible. On the red and white varieties, on gooseberries, and on wild 

 currants comparatively little damage is done, but black currants suffer 

 so severely at times that the disease promises to become quite a serious 

 pest in black currant plantations. 



The spores shed by the blisters on the pine in the spring are not known 

 to be capable of infecting other pines again, but they readily infect nearby 

 currants. The leaves only of the currant plant are attacked, and ten to fifteen 

 days after infection there appear on the under sides of these leaves small 

 pustules of a brilliant orange color, and filled with orange spores. These 

 spores in their turn are carried by the wind to other currant leaves and 

 thus the currant infection is spread throughout the summer. So rapid 

 is the spread of the disease by means of these spores that where currant 

 plantations are numerous in a district all the black currants for several 

 miles around the infected pine may be rusted before the end of summer. 

 Although the spores produced in the early part of summer on currant 

 leaves are incapable of reinfecting pines, yet towards the close of the 

 season the pustules put out small orange finger-like growths on which 

 spores are formed that are able to infect pines again; and since as noted 

 above the rust may spread on currants for several miles, there is every 

 danger that a new lot of pines may be infected a long distance away from 

 the original pine from which the currants received their infection in the 

 spring. 



So far as we yet know, the rust on the currants dies out each winter, 

 and infection has to start each spring from some blister canker on a pine 

 in the neighborhood. I would say, however, that several circumstances 

 arose during the course of our observations on this rust last summer, which 

 give grounds for suspecting that in exceptional cases the fungus may over- 

 winter on the currant. If these suspicions should finally be justified, the 

 problem of controlling the disease will be much complicated. 



