182 A Monograph of the Erysiphaceae 



New Zealand. 



Australia : Victoria (225). 



North America ; United States — Maine, Massachusetts, New 

 York, Pennsylvania, Maryland, New Jersey, Delaware, Virginia, 

 Carolina, Ohio, Michigan, Indiana, Alabama, Illinois, Mississippi, 

 Wisconsin, Missouri, Iowa, Minnesota, South Dakota, Nebraska, 

 Kansas, Montana, Idaho, Wyoming, Colorado, Utah, Nevada, 

 California, Washington ;— Canada, New Brunswick, Ontario, Mani- 

 toba. 



E, polygjjii {E, communis and E, Marlii of most authors) is the 

 commonest and the most variable species of the Erysiphaceae. As 

 may be seen from the specific description given above, the present 

 species is variable in every character ; nature of the mycelium, size 

 of the perithecium, number, length, color, etc., of the appendages, 

 number of asci and spores. It may seem, at first sight, undesira- 

 ble to allow so wide a range of variation to a single species, yet 



from the study of a very considerable amount of material it has 

 seemed to me impossible — so closely are the extreme forms linked 

 to the type — to separate any of these forms as varieties, much less 

 as species. As a matter of fact, although several forms here in- 

 cluded under E, polygoni have been separated as distinct species, 

 E. polygoni itself has been frequently confused with E. cichoni' 

 cearum, as a glance at any large herbarium will show. Before 

 attempting to separate and give names to the most striking: forms 

 of h. polygoni, it seems to me wiser to collect the vast number of 

 forms of the two mildews (recorded as parasitic on no less than 602 

 species of plants) round the two specific centers here distinguished 

 as E. polygojii and E. cichoraceanim. 



Moreover the forms which have been hitherto separated from 

 E. polygoni z.?, distinct species are certainly not satisfactorily defined. 



E. Martii [E. pin) still appears in many works as distinct from 

 E. polygoni, although the name appears practically to be one ap- 

 plied to examples of E. polygoni on certain host -plants quite as 

 much as to a form based on any morphological characters. Ori- 

 ginally, £. Martii was distinguished from "^. covimunis" by 

 LeveiUe on the ground of possessing colorless appendages ; De 

 Bary, however, finding that this supposed character did not hold 

 good, united the two, and many subsequent authors followed this 



