426 FUNGOUS DISEASES OF PLANTS 



infection is severe, but it is upon the fruit that the fungus be- 

 comes, in many sections of the United States, a serious disease. It 

 is far more common in regions of considerable humidity, but owing 

 to the fact that teleutospores are produced during wet weather, infec- 

 tion is usually immediately assured upon the pomaceous hosts in 

 the vicinity. The fungus has been noticeably abundant in apple- 

 growing regions in the eastern Appalachians and in the South. 

 Varieties of apples differ greatly in their susceptibility. In the far 

 West, crosses between the wild crab apple and the cultivated species 

 have given some forms peculiarly susceptible. The gall formation 

 on the cedar commonly attains a diameter greater than 2 cm., and 

 when the horn-like gelatinous sori are developed, the mass from 

 edge to edge may measure 8 cm. The teleutospores are 46-60 x 

 15-20^. 



XXII. GYMNOSPORANGIUM : OTHER SPECIES 



Gymnosporangium clavariseforme (Jacq.) Rees is a species un- 

 usually abundant in the northeastern United States. The teleuto- 

 sporic form occurs on the common or dwarf juniper (Juniperus 

 communis). Slight enlargements of the twig are produced, and the 

 sori are orange-red in appearance. In America the aecidia occur 

 on the hawthorn (Cratcegus tomcntosd), while in Europe they are 

 also produced upon Cratcegus oxyacantha, Cratcegus monogyna, 

 Pyms communis, and occasionally other pomaceous trees. This 

 species is apparently not so fixed in its specialization with respect 

 to hosts for the aecidial stage as other members of this genus. 



Gymnosporangium globosum Farl. This species produces on 

 the red cedar {Juniperus virginiana) smaller cedar apples than the 

 preceding, and they are also distinguished from the latter by the 

 texture of the gall, the deeper color of the spore masses, and cer- 

 tain spore characters. 



This fungus is a chief cause of the apple rust of the New 

 England States, and the rcestelia stage is also found on the pear, 

 quince, and some varieties of mountain ash. 



Gymnosporangium Sabinae Plowr., which is closely related to 

 Gymnosporangium globosum, has also the same coniferous host. 

 The aecidial stage has for some time been recognized as injurious 

 to pear culture in Europe. 



