THIELAVIA 159 



Microsphaera bonicerae, Wint. ( = M. alni, var. lonicerae, Salm.) 

 forms white mildew on the leaves of honeysuckle, but does 

 no appreciable injury. 



Perithecia globoso-depressed, blackish, appendages once to 

 twice as long as diameter of perithecium, 3-4 times forked 

 at the tip; asci 2-7 ; spores 3-6, 20-24 X 10-12 /z. 



Microsphaera berberidis (Lev.) forms white patches of mildew 

 on the leaves of barberry and Mahonia. 



Perithecia generally scattered, appendages having the tips 

 four times forked, branchlets straight ; asci 4-9 ; spores 

 4-6 in an ascus, 18-20X9-10 /*. 



ERYSIPHE (D. C.) 



Perithecia subglobose, appendages, simple or irregularly 

 branched, closely resembling the mycelium. Asci several, 

 2-8-spored. 



Recognised by the simple or vaguely branched appendages, 

 which much resemble the mycelium, with which they are 

 intermixed. 



Erysiphe polygoni (D. C.) forms a white mildew on the 

 leaves of cultivated peas, turnips, etc., and on various wild 

 plants. 



Mycelium variable in quantity, sometimes only forming a 

 thin film, at others dense ; perithecia gregarious or crowded, 

 small, appendages very variable, coloured, irregularly branched; 

 asci variable in number, size, and shape, containing a variable 

 number of spores, usually 3-6, 19-25 X9-14 ji. 



Mildew on oak. As a rule the oidium occurring on oak 

 leaves is rare, and for many years in succession is entirely 

 absent, but during 190S there was a serious epidemic both in 

 this country and on the Continent, not only the vigorous 

 shoots from stools, the parts most usually attacked, but also 

 the leaves on the younger branches of old trees. Not a single 

 ascigerous fruit was observed anywhere, hence the species to 

 which the oidium stage belongs is uncertain. 



THIELAVIA (Zopf) 



Perithecia globose, minute, asci many, ovate, 8-spored ; 

 spores elliptical, continuous, coloured. 



Two or three conidial conditions known= Torula basico/a 

 (Berk.) ; Miloivia nivea (Mass.), etc. 



