Erysipiie 223 



teresting form (occurring on young twigs of AIiiiis incana in Fin- 

 land) published as a distinct species, E, vcDialis^ by Karsten, but 

 which I have felt compelled to regard as only a form of E, poly- 

 goni, E. ciggregata can be separated from this form on the 

 twigs of Alnus in Europe only by the larger average size of 

 the perithecia and asci, and the greater number of the latter — 



characters of not very high specific importance. It is quite pos- 

 sible, I think, that E. aggregata may have to be considered only 

 a well-marked variety of ^. poIygo)n\ rather than a distinct species. 

 Valuable evidence on this point might perhaps be obtainable from 

 the experiment of sowing conidia of E, aggregata on host plants 

 of E. polygoni^ or conversely by infecting alder catkins with the 

 conidia of E. polygoni. 



8. E. TKIXA Harkn. [Figs. 141, 142] 



Erysiphc {ErysipJuIhx) trina Harkn. Bull. Calif Acad. Sci, 1:41. 

 1886; Sacc. Syll. Fung. Addit. ad Vol. I.-IV.: 3. 1886; 9: 370. 

 1 891; Burr, in Ell. & Everh. N. Amer Pyren. 14. 1892. 



Exsicc: Ell. & Everh. N. Amer, Fung. 2337 ; '^ Ell. & Ev^erh. 

 Fung. Columb. 23. 



Epiphyllous ; mycelium persistent, effused or forming irregular 

 patches ; perithecia minute, at first yellow^, becoming yellowish- 

 brown, globose, more or less gregarious, small, 52— 60/i in diam- 

 eter, averaging 1'^:^ fx, cells at first evident, 8-10 /i wide, soon be- 

 coming indistinct as the wall becomes semi-transparent ; appendages 

 usually 3 or 4, short and very rudimentary, sometimes apparently 

 absent; asci 3, very rarely 2, brodly ovate to subglobose, with or 

 without a minute stalk, 48--50 x 28-36/^; spores 2, large, some- 

 times slightly curved, 25—34 x 14-16/i. 



Host, — Querats agrifolia. 



Distribution. — North America : United States — California. 



E. trina is a very marked and interesting species, only known 



Q 



very 



folia. The perithecia are 

 turity ; the outer wall is very thin, membranaceous, and semitrans- 

 parent, so that the outline of the large spores is clearly visible in 

 the unopened perithecium (see Fig. 141). Although described as 

 without appendages, there are usually a few rudimentary ones 

 present at the base of the perithecium. 



Ji--. 



