112 THE NORTH AMERICAN SLIME-MOULDS 



This genus was by Link established on characters purely external. 

 Rostafinski supplemented Link's definition by calling attention to the 

 peculiar character of the capillitium and to microscopic characters in 

 general. The outer peridium is thick and strong, unlike the ordinary 

 structure in Physarum. Some physarums, however, have a very sim- 

 ilar outer wall; P. brunneolum, for instance; compare the perid- 

 ium of P. citrinellum. In dehiscence and structure there is also 

 some resemblance to some species of Diderma, and by Persoon and 

 Fries the common species was so referred, but the capillitium is again 

 definitive. 



A critical study of all these things really begins with Rostafinski's 

 microscope. Under his definition of the present genus P. squamulo- 

 sum Wingate and P. albescens Ell. might well be entered here. Such 

 course at present would but increase confusion, and until by future 

 research the ontogeny of all these, and so their relationship, shall be 

 more exactly known, the genus may be left with its historic species, — 

 montotypic. 



Leocarpus fragilis (Dickson) Rost. 



Plate VIII., Figs. 3, 3 a, i b. 



1785. Lycoperdon fragile Dickson, Fasc. PL Crypt. Brit, I., p. 25. 



1795. Diderma vernicosum Persoon, Ust. Ann. Bot., XV., p. 34. 



1809. Leocarpus vernicosum Link, Diss., I., p. 25. 



1875. Leocarpus fragilis (Dicks.) Rost., Mon., p. 132. 



Sporangia gregarious or clustered, sessile or stipitate, obovoid, 

 rusty or spadiceous-yellow, shining; peridium opening at maturity in 

 somewhat stellate fashion ; stipe filiform, white or yellow, weak and 

 short; spores dull black, spinulose, 12-14 fi. 



A common species, distributed through all the world, Iowa to 

 Tasmania. Recognizable at sight by the form and color of the 

 sporangia. In shape and posture these resemble the eggs of certain 

 insects, and, occurring upon dead leaves, generally where these have 

 drifted against a rotten log, they might perchance be mistaken for 

 such structures. With no other slime-moulds are they likely to be 

 confused. The outer peridium opens irregularly, or more rarely 



