Griffiths : Some Northwestern Erysiphaceae 139 



composites even to the naked eye ; and the number of asci and the 

 lighter colored appendages are also quite characteristic. Micro- 



sphaera diffusa and M. 



of separation, 



especially in the immature condition. After careful examination 

 of well authenticated specimens named by the describers, or dupli- 

 cate specimens of the type material, I have referred my specimens 

 on Lathyrus to M. Ravciidii and the forms on Vicia to M. diffusa. 

 Attention might be called in passing to the necessity of good de- 

 scriptions of the conidial stage of the Erysiphaceae as well as of the 

 perithecial one. Some of my material shows good characters in 

 the early condition of development. 



An interesting observation regarding the apparent sudden ap- 

 pearance of E. communis on several species of Polygomun is worth 

 recording. As stated before, the collection of fungi was begun in 

 South Dakota in 1892, but no specimens of E. communis were 

 found oxv Polygonum until 1895, when I found a few immature 

 specimens in the northern part of the state, and Mr. Williams re- 

 ported it from Brookings the same year. The next year more of 

 it was found, and in 1897 and 1898 it was abundant everywhere. 

 The fungus without doubt occurred on species of Polygonum long 

 before we happened to find it ; but that it occurred in small quan- 

 tity previous to 1896 there can be no doubt. 



It is interesting to compare the vertical distribution of these 

 species. This is governed mainly, no doubt, by the habits of the 

 hosts ; but as some of the host plants recorded here are found at 

 a much higher altitude and others at a much lower, the question 

 naturally arises as to the extent of aldtudinal influence. The fol- 

 lowing upper limits will be instructive : 



Erysiphe communis on Oenothera allncaulis, 6500 ft. 



Erysiphe cichoracearum on Mertensia Silnrica, 8500 ft. 



Erysiphe gramixis on Agropyron tcncrum, 8500 ft, 



MiCROSPHAERA VACCiNii on Vacctniuin JSIyrtillus ndcropJiyllum, 



S 5 00 ft. 



difoli 



Sphaerotheca humuli on Viola Canadensis, 7500 ft. 



The altitudes are all given for localities on Clear Creek in the 

 Big Horn Mountains in the vicinity of Buffalo, Wyo., where quite 

 a complete collection was made from the base of the mountains to 



T 



