40 THE NORTH AMERICAN SLIME-MOULDS 



This species is nearly related to P. citrine Hum by the nature 

 of the peridium, but differs in the size of the sporangia, the 

 habit of fruiting, size, color, and marking of the spores. It is 

 also related to P. mellcum, from which it differs in having no 

 columella, and most nearly to P. auriscalpium, from which it 

 may be distinguished by the much closer capillitium with paler 

 nodules, as well as by much stouter habit, and the peculiar 

 metallic or bronze yellow of the peridial wall. 



New York, Iowa. 



1 8. PHYSARUM DIDERMOIDES (Acharius) Rost. 

 PLATE IX., Figs, i, i a, \b, \c. 



1801. Spumaria (?) didermoides Acharius, Persoon, Syn. Fung., p. xxix. 



1829. Diderma oblongum Fries, Syst. Myc., III., p. 103. 



1831. Spumaria licheniformis Schweinitz, N. A. f., p. 261, No. 2364. 



1875. Physamm lividitm, var. licheniforme Schw., Rostafinski, Mon., 

 p. 96. 



1875. Physarum didermoides Acharius, Rost., Man., p. 97. 



Plasmodium pale watery white or gray ; sporangia crowded, 

 ovoid or cylindric, stipitate or sessile, blue gray, often capped 

 with white ; stipe variable in length and structure, where well 

 developed pure white, often flattened, expanded and diapha- 

 nous, connate with others through the irregular reticulate or 

 sheet-like hypothallus ; columella none ; capillitium ample, the 

 lime knots angular or rounded, white connected by hyaline 

 threads ; spores in mass black, by transmitted light dark violet, 

 decidedly spinulose, 12-15 /* 



A very variable species in many particulars. The sporangia 

 in the same cluster are stipitate and sessile, ovoid and spheri- 

 cal. Our description does not quite agree with that of Rosta- 

 finski. As may be seen from the plate, it is the outer peridium 

 that is with us white and burdened with lime, the inner is sim- 

 ple and comparatively thin. The snowy outer peridium is, how- 

 ever, easily displaced. The colony may not show it at all, in 

 which case the peridia remaining give to the fructification entire 

 a pale lead color, very characteristic. The disposition of the 



