24 BULLETIiSr 957, U. S. DEPARTMENT OF AGRICULTURE. 



which have been tested, the following are nearly immune: Eyath 

 Nova, Franco-German, Holland (see also Tubeuf, 174), London, 

 Rivers, Simcoe King. That is, plants tested under these names have 

 so far shown themselves resistant, but not entirely immune. 



The cultivated gooseberries, varieties of Rihes reclinatum in some 

 cases more or less mixed with American species of gooseberries, are 

 resistant but occasionally will become infected. 



Resistant species and varieties have been found reacting to the 

 fungus and affecting it as follows : 



(1) Decreased number of uredinia and telia. 



(2) Above accompanied by reduction in size of uredinia and telia with lowered 



viability . 



(3) Small streaks and flecks of dead or 'dying tissue in infected leaves with 



uredinia and telia. (See PI. V, fig. 1.) 



(4) Small dead spots formed earl}^ ^vith very few or no uredinia and telia. (See 



PI. V, figs. 3 and 4.) 



This agrees essentially with the results of Stakman (149) with 

 Puccinia graminis on resistant grains. 



LIFE HISTORY OF CRONARTIUM RIBICOLA. 

 The Peridermium Stage on Pines. 



THE INCUBATION PERIOD ON PINES. 



According to European investigators, Cronartium rihicola has an 

 indeterminate incubation period between infection of pine and pro- 

 duction of gecia. This varies from about two to four years, and 

 possibly much longer. In one of Klebahn's inoculation experi- 

 ments he got pycnial drops on young white pines 11 months after 

 the inoculation (71). In another instance, infection probably 

 occurred in 1887, pycnia were produced in 1888, and secia in 1889 

 (65). Recently Tubeuf (174) reported the results of successful 

 inoculations on Pinus strohus. Inoculations v^^ere made on Septem- 

 ber 11, 1914; pycnia formed in July, 1915; they were also produced 

 in 1916 in May and thereafter; secia appeared in April, 1917. 



In North America considerable attention has been given to this 

 matter. McCubbin (84) first attacked it by extensive studies of 

 naturally infected trees. He concluded that five seasons were 

 necessary for most of nearly 1,600 infections in Ontario to develop 

 mature secia. He outlines the process as follows: first season, 

 infection occurs; second season, dormant; third season, swelling of 

 the bark; fourth season, swelling with pycnia; fifth season, mature 

 secia. This makes a lapse of about three years and six months 

 between actual infection and the formation of mature secia. 



Stone (153) in 1917 studied this problem in a locality where the 

 fungus was fruiting on white pines for the first time after infection 

 occurred. The infection came from Rihes cynosbati, which in 1914 

 was heavily infected. The Ribes plants were removed in the spring 



