246 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



was not the case. After seventeen days yellow spots were ob- 

 ser\ed upon the Poiirthiaea and in five weeks aecia had developed, 

 while the other three species remained uninfected. While at 

 first this seems to be at variance with the previous results of 

 Shirai, it is comparatively easy to trace out the error in the work 

 of the latter. He had present on his culture material both a 

 stem and a leaf form. It can be said now without doubt that the 

 leaf-inhabiting form was responsible for his culture on Pyrus 

 sinensis. Not appreciating the possibility that he was dealing 

 with two species, a misinterpretation of his results was a very 

 natural outcome. The Roestelia produced on Pourthiaea by I to 

 is undoubtedly the one which was described by Henning in 1894 

 as R. Photiniae (Hedwigia 33: 231) and later referred to Gymno- 

 sporangium by the writer (Kern, loc. cit. 443). Accordingly, 

 G. japonicum, the stem form, is to be considered genetically re- 

 lated to R. Photiniae and not to R. koreaensis. In 191 2, Sydow 

 described an aecial stage on Cydonia vulgaris from Japan as G. 

 spinijerum (Ann. Alyc. 10: 78). It seems likely in the absence 

 of cultures that this should be regarded as a synonym of G. Pho- 

 tiniae. The small pale aeciospores agree perfectly. The peridial 

 cells agree well as to size and thickness of walls; the spines may 

 be somewhat coarser and longer in G. spinijerum but they do 

 not differ essentially. The peridium is longer and more robust in 

 G. Photiniae on Pourthiaea but none of the species which occur on 

 the leaves of Cydonia seem to be as robust on it as on the other 

 hosts. This is \'ery noticeable in G. Nidus-avis, a North American 

 species, which occurs on Amelanchier and Cydonia. The revised 

 synonomy and host list for this species would now be as follows: 



Gymnosporanc.ium Photiniae (P. Henn.) Kern, Bull. N. Y. Bot. 



Garden 7: 443. 191 1 

 Roestelia Photiniae P. Henn. Hedwigia 33: 231. 1894. 

 Gymnosporangiuni japonicum Sydow, Hedwigia 3 8: 141 (Bcibl.). 



1899. 

 Gymnosporangiiim spinijerum Sydow, Ann. Myc. 10: 78. 191 2. 



I. Aecia, with spiniferous peridial cells, on Cydonia vulgaris (L.) 

 Pcrs. and Pourthiaea villosa (Thunb.) Dec. {Photinia villosa Dec, 

 Photinia laevis DC.j. 



III. Telia, with spores 48-66 /u long, on the woody twigs and 

 branches of Juniper us chincnsis L. 



