138 A Monograph of the Erysiphaceae 



American authors. Examination of Berkeley & Curtis' type in the 

 Kew Herbarium shows the fungus to have these characters : "per- 

 ithecia 75-100 /^ in diameter, appendages 5-9, ^ to sHghtly longer 

 than the diameter of the perithecium, with the tips of the ultimate 

 branches, when mature, distinctly recurved ; asci and spores as in 

 M. alni. The appendages are mostly tinged amber-brown in the 

 lower half, and under low magnification there often seems asharpline 

 of demarcation between the colored basal part and the colorless up- 

 per portion. This appearance however, is due merely to the presence 

 of air in the colored basal part, and is common to several species 

 of Microspliaera and Uncinula. Sometimes, however, the appen- 

 dages are faintly colored throughout, and the plant then shows much 

 resemblance to '' M. erincophiia Peck," a form discussed below. 

 Apart from the more or less colored appendages the form on 

 CephalantJms is quite similar to many examples of M. alni on 

 other hosts, especially to the small form called by Leveille '' M. 



//...„., 



Burrill & Earle (61, p. 414} in their key to the genus Micro- 



sphaera place M. semitosta is the section " Tips of the appendages not 



recurved," and M. alni'm the section " tips recurved when mature." 



Burrill, too, says of M. semitosta, " tips obtuse not recurved." The 



mature apex, however, certainly shows recurved tips, and is, in all 



the specimens I have seen, quite similar in all respects to that of 

 M. alni. 



r 



It is worthy of note that Burrill says "primary branches 

 long"; so that it appears that the form on Cephalanthus sometimes 



forms mentioned later. 



Jap 



The only peculiarity, then, that distinguishes M. semitosta 

 is the more or less colored appendages. This character is, I am 

 quite convinced, insufficient to separate it from M. alni, being one 

 which, in the forms of this .species, cannot be considered of any 

 systematic value. In specimens of M. alni on Carya sulcata 

 (Urmeyville, Indiana, Coll. E. M. Fisher, 1890. Ex-IIerb. U. S. 

 Dept. Agric. n. 1 148 (specimen now in the Kew Herbarium)) the 

 appendages are usually colorless, or only fairly tinged, but occa- 

 sionally here and there one appendage shows a sharply marked off 

 colored basal part like that which occurs in the Cephalanthus form. 



