DIDERMA 129 



3. Diderma Persoon 



1794. Diderma Persoon, Rom. N. Mag. BoL, I., p. 89. 



1873. Chondrioderma Rost. Versuch, p. 13, Mon., p. 167. 



1894. Chondrioderma Rost., List, Mycetozoa, p. 75. 



1899. Diderma Persoon, Macbr., N. A. S., p. 92. 



Sporangia plasmodiocarpous or distinct, sessile or stipitate; the 

 peridium as a rule double, the outer wall generally calcareous with 

 the lime granules globular, non-crystalline, the inner wall very deli- 

 cate and often, in the mature fructification, remote from the outer; 

 columella generally prominent. 



The genus Diderma is usually easy of recognition, by reason of its 

 double wall, the outer, crustaceous, usually calcareous, and its limits 

 remain substantially as originally set by Persoon. His definition is as 

 follows : — 



"Peridium ut plurimum duplex; exterius fragile; interius pellucens, 

 subdistans. Columella magna, subrotunda. Fila parca latentia." — 

 Syn. Meth. Fung., p. 168. 



Rostafinski changed the name of the genus to Chondrioderma 

 {chondri, cartilage), seemingly at De Bary's suggestion, and seems to 

 have regarded Persoon's definition as applicable to those species only 

 in which the wall is not only plainly double, but in which the two 

 walls are as plainly remote from each other. More especially he 

 esteemed a new generic name necessary, since he regarded several in- 

 cluded species, as D. spumarioides, D. michelii, etc., monodermic. 



Since it is doubtful whether any diderma is really monodermic, and 

 since Persoon's definition in any case seems sufficiently elastic, we 

 have seen no reason to discard the older name. Persoon's Diderma 

 when established, /. c, included D. florifor?ne. He made some con- 

 fusion in his later work by admitting some physarums. This induced 

 Schrader to throw all the didermas into his new genus, Didymium. 



According to the nature of the sporangia! wall, the species fall 

 rather naturally into two sections: — 



A. Outer sporangial wall distinctly calcareous, fragile; species generally 



sessile Diderma 



B. Outer sporangial wall cartilaginous, the inner less distinct, or concrete 



with the outer; species oftener stipitate . . . Leangium 



10 



