18G A Monograph of the Erysiphaceae 



densa — although so marked in its extreme state — can be given 



even a varietal rank. Nothing can be more marked, at first sight, 

 than the forms of E. taurica with persistent densely compacted 

 mycelium, yet we find that this species may not uncommonly occur 

 with an evanescent mycelium ; in the same way we must, it seems 

 to me, considering the evidence afforded by the forms on Lirio- 

 dendron^ Diervilla and Aristotelia^ allow to E, polygoni a similar 

 range of variation in mycelial characters. 



Karsten, in the second part of Myc. Fenn. has described a 

 species o{ Erysiphc as follows : ^'E. vernalis Karst. Mycelium arach- 

 noideum, saepissime evanidum. Asci in quovis perithecio 8 

 ovoideo-sphaeroidei, breviter pedicellati 8-spori. Appendiculae 

 sat longae, cum mycelio intertextae. Hab. In ramulis vivis 

 Alni incanae fine mensis Majl ad Mustiala semel obscrvata. 

 A sequente \_E. Martii Lev.] fort3 non distlncta." In the No- 

 tiser ur Sallsk. Faun. Fl. Fenn. Forh. 13: 247 the following 

 further description is given, " Perithecia hcmisphaerica, mycelio 

 emersa, fusca, latit. circiter o. I mm. Asci 8ni. brevissime pedicel- 

 lati, ovoidei- vel oblongato-sphaeroidei, longit. circit. 69 mmm., 

 crassit, circit. 39 mmm. Sporae Snae, sphaeroideo-ellipsoideae, 

 longit. 16-18 mmm., crassit. 11-12 mmm. Appendiculae hy- 



ah'nae. . . . Species quasi media inter Erys. graminis at Erys. 

 Martii. ' ' 



Professor Karsten has kindly sent me specimens (now in the 

 Kcw Herbarium) of E. vernalis, and after a careful study of the 

 plant and comparison of it with numerous forms of E. polygoni, I 

 do not see by what characters it can be separated from this spe- 

 cies. It is, nevertheless, a rather marked and extremely interest- 

 ing form. The fungus occurs on the young shoots of Alims incana ; 

 the mycelium is more or less evanescent on the intcrnodcs, and the 

 perithecia are here scattered, but at the base of the buds the perithecia 

 become gregarious, and the mycelium is persistent. The perithecia 

 average about 1 20 /^ in diameter, and the appendages are rather 

 long, not much interwoven, hyaline and quite similar in every wa}' 

 to those of many forms of E. polygoni. The asci are usually rather 

 numerous, sometimes as many as 15, and may reach to 80 n in 

 length ; in shape they are usually broadly-ovate to ovate-oblong ; 

 very rarely, however, they show a tendency to become subcylin- 



