DIDERMA 135 



American students mistake larger and more globular forms of some- 

 thing else, of D. spumarioides Fr., whose spores are but little larger; 

 or of D. effusum (Schw.) Morg., where the flattened plasmodio- 

 carps anon splatter out to globose drops of polished whiteness, and 

 whose spores are 8 fi. But even here the chances of error are small. 

 In the species last named the columella or sporangial base is aluta- 

 ceous, not white; in Fries' species, while the columella if present may 

 be white, the peridial walls are different, difficult to distinguish. 



For these reasons, D. globosum Pers. may stand, waiting further 

 light from Europe. 



5. DiDERMA CRUSTACEUM Peck. 



Plate VII., Fig. 7 



1871. Diderma crustaceum Peck, Rep. N. Y. Mus., XXVI., p. 74. 

 1889. Chondrioderma crustaceum (Peck) Berl., Sacc, VII., p. 373. 



Plasmodium at first watery, colorless, becoming at length milky 

 white; sporangia closely crowded or superimposed, in a cushion-like 

 colony, creamy white, globose, imbedded in the substance of the 

 hypothallus, the outer peridium smooth, delicate, crustaceous, fragile, 

 remote from the blue iridescent inner membrane; hypothallus promi- 

 nent ; columella variable, generally present, globose ; capillitium dark- 

 colored, the threads branching and combining to form a loose net; 

 spore-mass black, spores by transmitted light dark violaceous, deli- 

 cately roughened, 12-15 fi. 



Common. Readily to be distinguished from the preceding by the 

 larger spores and more crowded habit. New England west to 

 Nebraska. 



The didermas are generally delicately beautiful. The outer wall 

 in the present species is like finest unglazed china, softly smooth, and 

 yet not polished, often absolutely white, with porcellanous fracture. 

 An inter-parietal space separates the outer from the inner wall, so 

 that the former may be broken, bit by bit, without in the least dis- 

 turbing the underlying structure. The inner wall is ashen or gauzy 

 iridescent green, sending back all colors in reflected light. The 

 spores are violet, deeply so when fresh, the capillitium strong and 

 likewise tinted; the columella passing down and blending with the 



