DIDERMA 131 



by a delicate, white, calcareous crust; the columella simply the base 

 of the plasmodiocarp, thin alutaceous; the capillitium pale, consisting 

 of short threads somewhat branched toward their distal extremities; 

 spores smooth, pale violaceous, 8-10 /x. 



This is Physarum effusum Schw., vid. N. A. F., No. 2297. It is 

 reported by Morgan from Ohio, and we have one specimen from 

 eastern Nebraska, so that it is probably of general distribution in the 

 eastern United States. 



This species was in the previous edition distinguished from the 

 Rostafinskian P. reticulatum with spores a little smaller, 6-8 jx, and 

 with a much stronger tendency to the formation of definite sporangia, 

 elongate indeed and branching but often globose or depressed globose. 

 This we may know as, 



Var. RETICULATUM Rost. 



1875. Chondrioderma reticulatum Rost., Mon., p. 170. 



1894. Diderma reticulatum (Rost.) Morg., Jour. Cin. Soc, p. 71. 



Sporangia gregarious, generally rounded, not much depressed, flat, 

 sometimes, especially toward the margin of a colony, elongate, venu- 

 lose or somewhat plasmodiocarpous, dull white, the inner peridium 

 ashen or bluish, remote from the calcareous crust, which is extremely 

 fragile, easily shelling off; columella indistinguishable from the base 

 of the sporangium, thin, alutaceous; capillitium of short, generally 

 colorless, delicate, sparingly branching or anastomosing threads per- 

 pendicular to the columella; spores black in mass, by transmitted 

 light violet-tinted, smooth, 6-8 fi. 



Perhaps our most common form. Found in fall on dead twigs, 

 leaves, etc. Recognized by its rather large, white, depressed or flat- 

 tened sporangia tending to form reticulations, and hence suggesting 

 the name. The lines of fruiting tend to follow the venation of the 

 supporting leaf; where the sporangium is round, the columella is a 

 distinct rounded or cake-like body; where the fruit is venulose, the 

 columella is less distinct. 



By these rounded forms we pass easily, as by a gate, to D. hemi- 

 sphericum, which, when wholly sessile, differs still in greater diam- 

 eter of the sporangia and in having somewhat larger spores. Usually 



