14 Raymond J. Pool 



sometimes gregarious, globose-lenticular, 160-225/x in diameter, 

 averaging 190^, cells obscure, irregular, 10 X H/* wide; appen- 

 dages very numerous, usually densely crowded, a little shorter 

 than the diameter of the perithecium, simple, smooth, aseptate, 

 thin-walled and hyaline throughout, tip simply uncinate ; asci 

 10-26, usually about 15, narrowly ovate or cylindrical, with or 

 without a short pedicel, 68-86X29-40^; spores 8, 18-22 X 10- 

 14/*. 



On: Acer saccharinum. 

 Burwell, Crete, Lincoln, Wabash, Weeping Water. 



Sometimes the appendages in this species are scarcely if at 

 all uncinate and are more or less irregular. Perithecia with ap- 

 pendages of this nature are about as common with us as those 

 with the typical form. Such specimens might possibly be mis- 

 taken for those of a species of Erysiphe. 



MlCROSPHAERA Lev. 



Perithecia globose to globose-flattened ; asci several, two to 

 eight spored ; appendages free from the mycelium, branched at 

 the tip in a definite manner, usually several times dichotomously 

 divided and very often ornate. 



KEY TO THE SPECIES 



I. Appendages much contorted and angular, branches very irregular and 



flexuous M. euphorbiae 



II. Appendages not as above. 



1. Appendages regularly dichotomous, tips recurved. M. alni 



2. Appendages openly dichotomous, colored, tips not recurved, 



M. russelUi 



3. Appendages colorless, not penicillate. 



1) Branches lax, irregular, ultimate branches long, 



M. diffusa 



2) Branches closer, regular, ultimate branches short, 



M. grossulariac 

 MlCROSPHAERA EUPHORBIAE (Peck) B. & C. 



Erysiphe euphorbiae Peck. 



Amphigenous ; mycelium usually sub-persistent, thin and ef- 

 fused, sometimes evanescent ; perithecia often gregarious in floe- 

 cose patches, sometimes scattered, 85-145/x in diameter, rarely 180^ 

 globose-depressed, cells 10-15^ wide; appendages 7-28, 2%-8 

 times the diameter of the perithecium, always flexuous and no- 



72 



