2$8 PLANT DISEASES 



produce the aecidium condition on pear leaves, but do so 

 readily on leaves of the medlar, quince, and hawthorn. 

 The aecidia, or cluster-cups, are cylindrical and soon split 

 into shreds; they appear on roundish, thickened, orange 

 spots, which are often bounded by a reddish or purple 

 line. 



Plowright, Brit. Ured. and Ustilag., p. 232. 



Fischer, Zeitschr.f. Pflanzenkr., vol. i. pp. 193 and 283. 



MOUNTAIN ASH CLUSTER-CUPS 



{Gymnosporangium juniperinum. Winter.) 



This is the fourth species having its teleutospore stage 

 parasitic on Juniperus communis and f. nanus. It is 

 recognised by the subglobose shape of the soft, gelatinous 

 spore- masses formed in spring, which are dark brown at 

 first, changing to orange at maturity. The aecidium stage 

 grows on living leaves of the mountain ash, and is also said 

 to have been found on apple leaves. The aecidia are 

 cylindrical and curved, soon becoming torn into shreds 

 at the tip. They occur in small clusters on orange-red, 

 roundish spots. 



Plowright, Brit. Ured. and Ustilag., p. 235. 



RASPBERRY RUST 



(Phragmidium rubi-idaei, Winter.) 



This fungus produces its three forms of fruit on the same 

 host-plant. The aecidium stage is the first to appear, and 

 may be found in June under the form of small yellow or 

 greenish-yellow pustules, usually arranged in circles on the 



