56 THE MYXOMYCETES 



display an inner peridium; forms globose with narrow base, but apex 

 cleft, and forms ellipsoidal, yet compressed, opening like the gaping of 

 some tiniest bivalve. Some of the shorter forms become obovate, the 

 bases so constricted as almost to constitute stipes. Surely variation in 

 the same plasmodium can go no farther ! 



Cosmopolitan. Widely distributed in the United States and often 

 common. Frequent in Europe and reported from all continents except 

 Australia. We have a collection, however, from Samoa. 



19. Physarum bitectum List. 



Mycetozoa ed. 2. 78. 1911. 

 PI. IV, Figs. 55, 56. 



1891. Physarum diderma List., Jour. Bot. 29 : 260, non Rost. 



Sporangia gregarious, some subglobose and sessile, mostly plasmo- 

 diocarpous, smooth, white or pallid, terete or somewhat compressed; 

 peridium double, the outer wall calcareous, free and deciduous above, 

 recurved and persistent below, the inner smooth, pale purplish, more 

 persistent; dehiscence more or less irregular beginning at the top; 

 capillitium of large white nodules connected by short hyaline tubes; 

 spores violaceous brown, spinulose, with a conspicuous smoother area, 

 10-12 ii. 



Related to P. bivalve, but differing in the purplish inner wall, the 

 larger, rougher spores, and the less compressed fructifications. The 

 latter character is variable in both species. 



Colorado and Montana to the Pacific coast, not rare, Venezuela; 

 Europe, South Africa, Australia. 



20. Physarum diderma Rost. 



Mon. 110. 1875. 

 PL IV, Figs. 60, 61. 



1898. Physarum didermoides Rost. var. lividum Lister, Jour. Bot. 36 : 162. 

 1907. Physarum testaceum Sturgis, Colo. Coll. Pub. Sc. Ser. 12 : 18. 



Sporangia snow-white, clustered, sessile or narrowly adnate, globose 

 or polygonal by mutual compression; peridium double, the outer layer 

 dense, fragile, thick, calcareous, the inner delicate, remote, translucent; 

 capillitium well developed, the calcareous nodules white, rounded or 

 angular, sometimes uniting to form a pseudocolumella; spore-mass 

 black; spores purplish, distinctly rough, 10-12 fx. 



A beautiful and distinct species. As others in the group with which 



