56 A Monograph of the Erysiphaceae 



A few words of explanation are necessary in connection with 

 the names here adopted for the two plants. Erysiphe hiamili DC. 

 (1815), being the oldest name of either of the two, must stand as 

 the specific name of the plant here considered the type and called 

 5. kuumli (DC.) Burrill. The other plant has, as already men- 

 tioned, been called 5. Castagnei Lev. by Burrill, but this name 

 cannot be retained, and the oldest name Alphitomorpha fidiginea 

 Schlecht. (18 1 9) must be adopted in its place. It is true that in 

 Schlechtendal's description the large cells of the perithecium, 

 which form the essential character of the variety, are not mentioned, 

 so that the identity is established solely by means of the host- 

 plant ( Veronica) given. As, however, we know that on this host 

 it is exclusively the large-celled form which occurs we can safely 

 adopt the name fuIginca—]M?>t as has been already done In fact, 

 in the similar case of " Erysiphe Immuli " on the hop. 



A form of .S". hiivmli which occurs on Pyrus Aria has been 

 described as a distinct species by de Thuemen under the name of 

 5. Nicsslii. The separative characters relied upon were the smaller 

 perithecium and ascus, and especially the scattered habit ot the 

 plant. In examining a large series of 5. hiuimli, however, it is 

 seen that the characters given cannot be considered distinctive of 

 the form on Pyrus Aria alone as we find examples on many other 

 hosts, e. g., on Potcntilla, in which exactly the same habit is found. 

 In specimens on Potcntilla, just as in " S. Nicsslii'' on Pyrus Aria, 

 the appendages of the perithecium tend to become obsolete, per- 

 haps owing to the densely tomenlose surface of the host-leaf in 

 both cases. The perithecia of "5. Nicsslii " that I have examined 

 average^ 60 ^ in diameter (de Thuemen stated the average to be 86 

 /i). This is rather below the usual size for 5. /mj;n/li, but perithecia 

 of the same size do occur on Potcntilla and other hosts, with asci o, 

 as small a size as that given for " 5. Nicsslii." It rmy be noted too! 

 that in 5. kumuli var. fidiginca perithecia with a diameter of only 

 50 li occur. On the whole. " ^. NicssUr cannot be regarded as 

 anything more than a small form of 5. Jmmidi. 



E. epilobii is identical w^ith certain forms of 5. humuli. No 

 sufficient distinguishing characters have been given in any diagnosis 

 of this form, and it is evident that, as a general rule, specimens 

 have been referred to "5. epilobii" merely from their occurrence 

 on species of Epilobium. 



