118 THE MYXOMYCETES 



Sporangia plasmodiocarpous, hemispherical or turbinate, sessile or 

 very short-stalked, cream colored or white; peridium double, the outer 

 shell-like, the inner membranaceous, more or less adherent to the 

 outer, both caducous together, leaving the thickened base surrounding 

 an expanded columella; stipe, when present, very short, stout; capilli- 

 tium colorless, nearly simple; spores brownish purple, strongly warted, 

 9-10 /x. 



On straw, decaying leaves, especially succulents such as Agave, 

 and on decaying cactus stems. 



Said to be common in England, occurring also in Portugal, Algeria, 

 Japan. The only American collection thus far seems to be one made by 

 Bethel, at Monrovia, California, on the usual substrata. 



19. Didymium listeri Massee 



Mon. 244. 1892. 

 1894. Didymium dubium Rost. ex Lister, Mycetozoa 95, in part. 



Plasmodiocarp pulvinate-compressed, thin, occurring in irregular 

 scattered patches 3-7 mm. in extent; outer wall white, shell-like, 

 covered with a powdery layer of stellate crystals, the inner peridium 

 delicate, membranous, dark, adherent, the whole tending to break 

 away entire, leaving the mass of spores and capillitium exposed; 

 columella none; capillitium dense, threads parallel, rarely over 200 n 

 long, branching acutely and dichotomously and connected by trans- 

 verse bars, dark brown, the tips paler; spores globose, dingy lilac, 

 minutely warted, 8-11 ix. 



Formerly confused with D. dubium Rost., which, however, has much 

 larger spores and a different peridium. See that species, also Journal 

 of Botany 64 : 226, 1926. 



Iowa, Bermuda; Great Britain, Germany. 



20. Didymium difforme (Pers.) Duby 



Bot. GaU. 2 : 858. 1830. 

 PL VIII, Figs. 172, 173. 



1797. Diderma difforme Pers., Tent. Disp. Meth. 19. 



1803. Licea ccesia Schum., Enum. PL Saell. 2 : 219. 



1809. Physarum difforme Lk., Mag. Ges. Nat. Fr. Bed. 3 : 27. 



1813. Amphisporium versicolor Link, Mag. Ges. Nat. Fr. Berl. 7 : 41. 



1817. Didymium cyanescens Fr., Symb. Gast. 19. 



1823. Licea alba Nees, in Kunze & Schmidt Myc. 2 : 66. 



1823. Lycogala minutum Grev., Scot. Crypt. Fl. 40. 



1825. Reticularia pusilla Fr., Syst. Orb. Veg. 1 : 147. 



1829. Diderma cyanescens Fr., Syst. Myc. 3 : 109. 



1829. Physarum album Fr., Syst. Myc. 3 : 147. 



