8 Raymond J. Pool 



Erysiphe tridactyla Tul. 



Amphigenous ; mycelium evanescent, sometimes sub-persistent ; 

 perithecia scattered, or more or less gregarious, sub-globose, 70- 

 100 (a in diameter, cells 10-15 /x wide; appendages 3-10, usually 

 only 4-5, springing in a cluster from the apex of the perithecium, 

 more or less erect, septate, tips 3-5 times dichotomously branched 

 primary branches elongated, ultimate branches rounded or more 

 or less knob-like; ascus globose, 60-80 X 60-70^ ; spores 8, 20- 

 30 X 12-1511. 



On : Prunus americana, P. ccrasus. 

 Lincoln, Wabash, Weeping Water, York. 



The apical insertion of the more or less erect appendages is 

 the character which usually separates this species from P. oxya- 

 canthac It is a question whether this is sufficient ground for 

 making a species for the form, and I have had some hesitation in 

 assigning specific rank to P. tridactyla since it is usually regarded 

 as a variety of P. oxyacanthac. Salmon regards it as a variety 

 of the latter, and remarks : " The published records of Podo- 

 sphacra tridactyla (Wallr.) from America almost certainly all be- 

 long to P. oxyacanthac, as the former name has been in error, 

 commonly used by American mycologists as a synonym of the 

 latter species." However the two forms seem sufficiently differ- 

 ent to warrant the above treatment in this place. The two forms 

 should be studied further from local material. 



Podosphaera leucotricha (Ell. & Ever.) Sal. 



Spliacrotheca leucotricha Ell. & Ever. 

 Sphacrothcca mail Burrill. 



Amphigenous ; mycelium persistent on the young stem, the 

 petioles, and leaves, effused ; perithecia densely gregarious, rarely 

 scattered, 75-90/x, in diameter, cells io-i6/x wide; appendages of 

 two kinds, the apical ones 3— II, 4-7 times the diameter of the 

 perithecium, becoming thick-walled, dark brown in the lower 

 half, pale toward the tip, tip undivided or blunt, rarely once or 

 twice dichotomously divided ; basal appendages short, tortuous, 

 pale brown, simple, or irregularly branched ; ascus oblong to sub- 

 globose 55-70 X 44-50/x, ; spores 22-26X12-14^. 



On : This species is reported by Heald in the nineteenth annual 

 report of the Nebraska Agricultural Experiment Station 



66 



