414 Illinois State Laboratory of Natural History. 



the appendages average a little shorter than on Primus, but 

 they show no other appreciable differences. In both cases they 

 are too variable for this to constitute a distinguishing charac- 

 teristic. 



As our specimens thus present intermediate forms con- 

 necting those that are separated in Europe, it becomes necessary 

 to consider them all as belonging to one variable species. 

 Widely varying species are common among the Erysi- 

 phece, and the forms included here differ much less widely than 

 those that are referred to Erysiphe communis or Phyllactinia 

 suffulta. As De Candolle's name has priority, it must be re- 

 tained. 



MlCROSPH^ERA, LEV. 

 (Ann. Sci. Nat., Ser. III., Tome XV.) 



Perithecium containing several asci; appendages free from 

 the mycelium, more or less dichotomously branched at the 

 end. 



KEY TO THE ILLINOIS SPECIES OF MICROSPH^RA. 



I. Tips of the appendages not recurved A. 



II. Tips of the appendages recurved when mature B. 



A. Appendages colored 1. 



Appendages hyaline or nearly so 2. 



1. Appendages short (equal to diameter of perithe- 



cium) M. SEMITOSTA. 



Appendages very long (4-6 times diameter of 

 perithecium ) M. RUSSELLII. 



2. Appendages medium (2-3 

 times diameter of perithe- 



M. DIFFUSA. 



M. SYMPHORICARPI. 



cium ) 

 Appen< 

 ameter of perithecium) \ M. EUPHORBIA. 



Appendages long ( 3-6 times di- j M. VACCINII. 



