PERIDERMIUM STROBI. 443 



The spores of this fungus germinate on the leaves and stem 

 of Vincetoxicurn qfficinale, Mnch., and on other species of Vince- 

 toxicum, producing the fungus, Peridermium Cornui, E. et 

 Kleb. The teleutospores from this again infect pines. As, 

 however, there is no Vincetoxicum in Britain, where pine- 

 blister is very common, there appear to be two forms of the 

 disease, one P. Cornui, E. et K., and the other P. Pini, Wallr., 

 the teleutospore form of which is unknown. 



b. Subjects of Attack. 



Scots and black pines of all ages are attacked by pine-blister, 

 but preferentially fifteen to twenty years old poles. It attacks 

 only organs two or more years old, and is commonly found at 

 verticils of branches and in the crown of the tree. It has 

 been often observed in mixed forests of pine with beech or 

 hornbeam, where the branches of the broadleaved species, 

 swayed by the wind, have rubbed off the bark of the pines. 



The disease is well known all over Europe west of Poland. 



c. Protective Measures. 



Fell infected pines as soon as the disease is noticed.* 



6. Peridermium Strobi, Kleb. 



(Weymouth Pine-blister.) 

 a. Description and Mode of Attack. 



The Weymouth pine-blister resembles the ordinary pine- 

 blister externally. It attacks the cortex of stems and branches, 

 and especially at the verticils, causing long swellings. .From 

 these, yellow pustules eventually break out, which on bursting 

 emit spores in a dark yellow powder. The mycelium grows 

 for years in the cortex, and produces blisters (secidia) every 

 year. The disease kills the stem and branches above the seat 

 of infection, and sometimes the tree. 



The disease is contracted by an intermediate host. This is 

 either a currant or gooseberry bush. Among the former, 

 Ribes niyrum, L., R. rubrum, L., and R. aureum, Pursh., are 



* See Klebahn, Dr. H., " Fbrstliche Blatter," 1891, p. 151. Id. Forstlich- 

 natuwissenschaftlicbe Zeitschrift, 1897, p. 334. 



