382 UREDINKAK. 



pierced by a circular opening under which lies the yellow 

 uredospore-patch of the Cronartium enclosed in its peridimn. 

 The ovoid yellow uredospores have a coat beset with short 

 spines and are abjointed singly from short cylindrical sporo- 

 phores (Fig. 215). From the uredo-sorus there next' arises a 

 protuberance which lengthens till it forms an elongated slightly 

 curved brown cone or column consisting of cylindrical teleuto- 

 spores firmly built together (Fig. 215). The teleutospores 

 germinate without becoming detached from the mass, and 

 produce a four-celled promyceliurn with small sterigmata from 

 which globular sporidia are abjointed. The sporidia on reach- 

 ing the branches of Scots pine produce in its bark at first 

 pycnidia, later aecidia. The pycnidia (spermogonia) give off' 

 yellow drops of liquid with a characteristic odour. The 

 aecidia are yellow thick- walled sacs ; their spores are set free 

 in spring and infect young plants of Cynanchum. 



Since the sporidia of the Cronartium -stage are shed by 

 September, the fungus would seem to hibernate only in the 

 form of mycelium in the branches of pine. 



The effects of this fungus on the pine will be considered 

 along with those of Pcridermium pini, another blister-rust 

 of pine closely resembling this species (p. 411). 



Or. ribicolum Dietr. Uredo- and teleutospores are developed 

 towards the end of summer on leaves of various species of 

 Ribes (e.g. Ribcs nigrum, nibrum, aureum, alpinum, sanguincum, 

 americanum, rotundifolium, setosum, and Grossularia). The 

 aecidium-stage (Pcridermium strobi Kleb.) forms the blister-rust 

 of the bark of Weymouth pine (Pinus Strobus). Pycnidia 

 appear in the summer of infection ; the aecidia a year 

 later. Externally this bark-rust resembles that of Peridermii/m 

 Cornui and P. pini on the Scots pine. It may cause con- 

 siderable damage to Weymouth pine both in nursery and 

 plantation. 1 



It is probable that other two forms of Accidium are identical 

 with this, viz., that on Pinus Lambertiana in America, and 

 P. Gemlrm especially in Paissia. 



Or. flaccidum (Alb. et Schwein.) (Britain and U.S. America). 

 Uredo- and teleutospores on Pai'<>ni, causing the leaves to dry 



1 Magnus (Gartenflora, 1891) has pointed out that both the Cronartium and 

 the Perii/i niii/im are unknown in America, the home of the Weymouth pine. 



