320 DISEASES OF CULTIVATED PLANTS 



fungus appears on living bark of the Weymouth pine {Pinus 

 strobus) ; it has also been recorded on Pinus lambertiana and 

 P. cembro. The aecidia are large, and burst through the 

 bark in great numbers, eventually opening and exposing a 

 powdery mass of orange spores. These spores germinate 

 readily on living leaves of the black currant {Ribes nigrum), 

 and first give origin to numerous sori or pustules of uredo- 

 spores ; from the centre of each uredospore sorus a slender 

 hair-like body develops, about one line long, consisting of an 

 agglutinated mass of teleutospores. At this stage the leaf 

 presents the appearance of being covered with a forest of 

 erect, slender hairs. The teleutospores germinate in situ, 

 and produce very minute secondary spores which in turn 

 give origin to the aecidium stage on pine bark, producing 

 spermogonia the first year and the aecidium condition the 

 following season. 



Although the Weymouth pine is of American origin, the 

 disease is unknown in that country. 



Aecidiospores large, one portion of epispore smooth, 

 remainder warted. Uredospores elliptical or ovoid, orange, 

 aculeate, 19-35 x 14-22 /x. Teleutospores forming a columella 

 1-2 mm. high, curved, yellowish rufous. 



As the fungus requires two hosts for its development, the 

 removal of one of these arrests the disease. 



Rostrup, Bot. Coiiralb., 43, p. 353. 



Pine blister-blight [Cronartium asclepiadeum, Fries. 

 (= Peridennium cornui, Rostr. and Klebh.). 



The aecidia appear on the bark of Scots fir (Pi/ius silvestris) 

 late in spring, bursting through the outer dead cortex as 

 irregular, inflated, pale yellow sacs, which open by an irre- 

 gular crack and liberate the powdery, orange spores. The 

 hair-like, elongated masses of teleutospores springing from 

 the uredo pustules grow on the under surface of the leaves of 

 Cynachum vincetoxicutn. 



Supposed varieties of this species occur on oaks {Quercus 

 nigra and Q. tincloria), also on Comandra umbellata and C. 

 pallida in the United States, also on leaves 1 >f . Isclepia speciosa 

 in France. 



Aecidiospores having the epispore partly reticulated and 

 partly warted, 22-26 /x, rarely 30 x 16-20 /*. Uredospores pale 

 orange, echinate, variable in form, 16-32X12-18 /x. Colu- 



