114 THE MYXOMYCETES 



close to certain small developments of the typical form to warrant 

 specific recognition. 



Colorado, Oregon, Washington; Germany. 



13. Didymium clavus (Alb. & Schw.) Rabenhorst 



Deutsch. Krypt. El. 1 : 280. 1844. 

 PI. VII, Figs. 154, 155. 



1805. Physarum clavus Alb. & Schw., Consp. Fung. 96. 



1829. Didymium melanopus Fr., Syst. Myc. 3 : 114. 



1873. Didymium commutabile Berk. & Br., Jour. Linn. Soc. 14 : 83. 



1892. Didymium radiatum Berk. & Curt, ex Massee, Mon. 229, in part. 



1892. Didymium neglectum Massee, non Berk. & Br., Mon. 231. 



1899. Didymium masseeanum Sacc. & Syd., Syll. Fung. 14 : 836. 



Sporangia gregarious, pale gray, discoid or pileate, depressed, stipi- 

 tate; peridium dark colored, frosted with calcareous crystals above, 

 naked below; stipe short, slender, tapering upward, furrowed, black, 

 arising from a more or less distinct hypothallus; columella obsolete; 

 capillitium of delicate threads, pale or colorless, little branched; spores 

 violaceous, pale, nearly smooth, 6-8 fx. Plasmodium gray. 



This species is well differentiated, easy of recognition by reason of 

 its peculiar discoid sporangium, calcareous above, naked and black 

 beneath. D. neglectum Massee, reported from Philadelphia, is said 

 to be a slender form of the present species. The figures of Albertini 

 and Schweinitz are excellent, as is their description. 



Occasionally collections occur in which the spores are distinctly 

 warted, with clusters of darker warts scattered over the surface. 

 These seem otherwise to be typical. Hohnel (1909) believes that 

 D. commutabile is a related but distinct species, characterized by a 

 long, white or yellowish and strongly encrusted stipe and by smaller 

 spores, 5-6 /x in diameter. 



Pennsylvania, Wisconsin, Ohio, Iowa, Washington, Bolivia, Brazil, 

 Argentina; Europe, Africa, East Indies, Japan and the tropics gener- 

 ally. Not common in the United States. 



14. Didymium melanospermum (Pers.) Macbr. 



N. A. Slime-Moulds 88. 1899. 

 PI. VIII, Figs. 164, 165. 



1794. Physarum melanospermum Pers., Roem. N. Mag. Bot. 1 : 88. 



1797. Didymium far inaceum Schrad., Nov. Gen. PI. 22. 



1797. Trichia compressa Trentep., Roth, Cat. Bot. 1 : 229. 



1797. Trichia depressa Trentep., Roth, Cat. Bot. 1 : 231. 



1799. Trichia sphcerocephala Sow., Engl. Fung. 240. 



1801. Physarum farinaceum (Schrad.) Pers., Syn. Meth. Fung. 174. 



