14 



BULLETIN 957, U. S. DEPAETMBNT OF AGRICULTURE. 



wounded. At this stage slugs ate the infected bark and prevented 

 further development of the fungus. In 1916 and in 1917, 150 

 seciospore inoculations were made on leaves, on twigs of various ages, 

 and on branches of P. strohus trees up to six years. No infections 

 have resulted. 



Clinton and Miss McCormick (14, 15), have published details of 

 successful inoculations, through the leaves, with sporidia on P. 

 strohus. Inoculations were unsuccessful upon leaves of P. excelsa, 

 P. Jlexilis, P. Jcoraiensis, and P. cembra; also on the pitch pines P. 

 resinosa, P. sylvestris, P. densijlora, and P. austriaca. Yellow spots 



Fig. 11. — Outltae map of the northeastern part of the United States, showing (by black dots and cross 

 hatching) the known distribution of white-pine bhster rust in North America to and including 1917. 



have been secured on leaves of P. lamhertiana, P. pinea, and P. 

 sahiniana. 



Cross-inoculations that are known to have been successful up to 

 July 1, 1920, are shown in Plate I. 



Species of Ribes That Have Been Infected NaturaUy. 



In Europe and North America, where extensive outbreaks of 

 Cronartium ribicola have occurred, a considerable number of species 

 of Ribes have been found naturally infected by the fungus. Prac- 

 tically all of the cultivated species and most of the wild ones take the 

 disease in every extensive outbreak area. More species have been 

 found infected in Europe than in North America, because outbreaks 

 have been discovered there in botanical gardens, parks, and nurseries 



