DiDYMIUM 129 



short, slender threads, rupturing in unison, and permitting the 

 plasmodiocarp to open as a whole for spore-dispersal. It is an 

 anomalous form, having lime in the capillitium like a Physarum, 

 but nevertheless a Z)^'^3'wnMm. The thin plasmodiocarps, appear- 

 ing in the field as smears on the bark, resemble a common fungus, 

 and may be easily taken therefor. The species probably forms 

 large plasmodia, as on one occasion we obtained hundreds of 

 plasmodiocarps from the bark of a single dead tree. 



15. Didymium anellus Morg. Jour. Cin. Soc. Nat. Hist. 16: 148. 

 1894. (N. Y. B. G. no. 13125, authentic material.) 



Plasmodium colorless (Lister). Sporangia scattered, sessile, 

 pulvinate or flattened, centrally depressed, 0.3 to 0.5 mm. diam., 

 often forming slender plasmodiocarps also depressed, elongate, 

 branched, netted or perforated, gray, glossy brown or iridescent 

 from the absence of lime; sporangial wall membranous, colorless 

 or purplish brown, with scanty deposits of small crystals of lime, 

 usually dehiscing in a circumscissile manner. Columella none. 

 Capillitium abundant, consisting of slender, flexuose, violet- 

 brown threads, simple or somewhat branching and anastomosing. 

 Spores purplish gray or purplish brown, minutely spinulose, 

 7-12 fx diam. 



Type locality: Ohio. 



Habitat: On dead leaves, herbaceous stalks, and twigs. 



Distribution: *California, Colorado, *Iowa, Kansas, *New 

 Mexico, New York, Ohio, Ontario, *Oregon, Pennsylvania, 

 Quebec. 



Illustration: Lister, Mycetozoa ed. 3. pi. 110, figs. a-c. 



This species has been collected repeatedly by experienced 

 students in their local areas, and is probably more widely dis- 

 tributed. The spores are very variable in their characters, so 

 that they, and also the capillitium, are of little aid as determining 

 factors. The shape and appearance of the sporangia and plas- 

 modiocarps, their usual association in one development, and the 

 circumscissile manner of dehiscence are the important features. 

 Sometimes large netted or perforated plasmodiocarps are found, 

 and these resemble similar plasmodiocarps of D. sqimmulosum. 

 Unless accompanied by sporangia of either species, they are often 

 indeterminate. The circular depressions in the sporangia, and 

 the linear ones in the plasmodiocarps of D. anellus, indicate that 

 the Plasmodium in forming spreads in rings which close and leave 



