162 A Monograph of the Erysiphaceae 



(324), Michigan, Alabama, Illinois, Mississippi, Wisconsin, Mis- 

 souri, Iowa, Minnesota, South Dakota, Kansas, Montana, Wyo- 

 ming, (Sub M, symphoricarpi) Pennsylvania, Virginia, Ohio, 

 Indiana, Illinois, Missouri, North and South Dakota, Kansas, 

 Montana, Idaho, Colorado, California, Washington. 



A species very variable in every character except the irregular 

 diffuse branching of the apex of the appendages, in which a good 

 specific distinction is found. The dichotomous nature of the branch- 

 ing ceases in the higher orders, so that the youngest branches are 

 irregularly arranged, and often appear as lateral outgrowths ; a 

 slightly nodulose appearance of the branches is also characteristic 

 of the present species (see Figs. 31, 32). 



After seeing a large amount of material, I feel convinced that 

 the plant on Synnplioricarpos — M. syniplioricarpi^ E. C. Howe, 

 should be referred to M, diffusa. In this form the perithecia are 

 perhaps sUghtly smaller on the average, although the size varies 

 greatly (I have seen contiguous perithecia on a leaf measuring 55 

 // and 104 j« in diameter) ; the appendages are usually fewer 

 (4-24), and tend to become longer than in typical M, diffusa; but 

 these characters are not constant. In certain specimens on Svin- 

 phoricarpos, perithecia taken from the same leaf show a variation 

 in the length of the appendages of from i ^ to 7 times the diameter 

 of the perlthecium ; while, on the other hand, M. diffusa on other 

 host-plants frequently possess appendages reaching to four times 

 the diameter of the perithecium,* and as few as 12 in number. In 

 the peculiar character of the apical branching of the appendages 

 the form on Symphoricarpos agrees well with M. diffusa, and as 

 this is, I consider, the most important specific character, I feel lit- 

 tle hesitation in treating the two plants as one species. It is nec- 

 essay to point out that in the form on Symplioricarpos the appen- 

 dages are very slow in reaching their full development, and unless 

 perfectly mature examples are examined, the apex of the appen- 

 dages appears less diffusely branched. In specimens with a fully 

 developed apex, however, as is the case, e. g,, with those on S. 

 occidaitalis (Fort Collins, Colorado (C. F. Baker)) and on 5. 

 racemosus (Datah Co., Idaho, June, 1897 (L. F. Henderson)) both 



*Burrill & Earle (6l, p. 417) mention specimens on Lespedeza capitata with 

 appendages " 5 or 6 times the diameter." 



