116 THE MYXOMYCETES 



D. nigripes by the shorter, thicker stem and the somewhat flattened 

 and more distinctly umbilicate sporangium. 



New England to Alabama and Nebraska, Washington; Europe, 

 Africa, Java, Japan, probably cosmopolitan. 



16. Didymium nigripes (Link) Fr. 



Syst. Myc. 3 : 119. 1829. 

 PI. VIII, Figs. 168, 169. 



1809. Physarum nigripes Link, Mag. Ges. Nat. Fr. Berl. 3 : 27. 



1818. Physarum microcarpon Fr., Symb. Gast. 23. 



1846. Didymium porphyropus Dur. & Mont., Fl. Alg. 409. 



1875. Didymium microcarpon (Fr.) Rost, Mon. 157. 



1888. Didymium tenue Pat., Bull. Soc. Myc. Fr. 4 : 96. 



Sporangia gregarious, globose or hemispherical, 0.3-0.5 mm. in 

 diameter, umbilicate beneath, white, stipitate; peridium smoky, cov- 

 ered with minute calcareous crystals; columella dark; stipe slender, 

 erect, black, opaque; hypothallus scutate, black; columella distinct, 

 globose, black or dark brown; capillitium of delicate threads, pale 

 brown or colorless, with occasional brown thickenings or nodes, spar- 

 ingly branched; spores pale, violaceous by transmitted light, minutely 

 warted, 7-10 /x. 



Rostafinski adopted Fries' name microcarpon simply because he 

 thought it more appropriate. Fries describes the columella "none 

 or . . . black." It is doubtful whether we have the typical Friesian 

 form on this continent. The fructification is in our specimens small, 

 about 0.4 mm., and the spores, as noted by Morgan, small; other- 

 wise the species is very close to D. xanthopus. Lister regards both 

 D. xanthopus and D. eximium as merely varieties of nigripes. 



New York, Ohio, Wisconsin, Iowa, Washington, Puerto Rico, 

 British Guiana, Bolivia, Argentina. Cosmopolitan. 



17. Didymium xanthopus {Ditmar) Fr. 



Syst. Myc. 3 : 120. 1829. 

 PI. VIII, Figs. 170, 171. 



1817. Cionium iridis Ditmar, in Sturm, Deutsch. Fl. 3 : 13. 



1817. Cionium xanthopus Ditmar, in Sturm, Deutsch. Fl. 3 : 37. 



1829. Didymium iridis Fr., Syst. Myc. 3 : 120. 



1829. Didymium pertusum Berk., in Sm. Eng. Fl. 5 (2) : 313. 



1873. Didymium proximum Berk. & Curt., Grev. 2 : 52. 



1892. Didymium microcarpon (Fr.) Rost. ex Macbride, Nat. Hist. Bull. Iowa 



2 : 146, in part. 

 1892. Didymium elegantissimum Massee, Mon. 243. 

 1925. Didymium nigripes Fr. var. xanthopus (Ditm.) Lister, Mycetozoa ed. 



3. 116. 



