DIDERMA 93 



" Peridium ut plurimum duplex ; exterius fragile ; interius 

 pelluceus, subdistans. Columella magna, subrotunda. Fila 

 parca latentia." - Syn. Metk. Fung., p. 168. 



Rostafinski changed the name of the genus to Chondriodenna 

 (c/wndri, cartilage), seemingly at De Bary's suggestion, and seems 

 to have regarded Persoon's definition as applicable to those spe- 

 cies 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 included species, as D. spwnarioidcs, 

 D. michelii, etc., monodermic. 



Since it is doubtful whether any Diderma is really mono- 

 dermic, and since Persoon's definition in any case seems suffi- 

 ciently elastic, we have seen no reason to discard the older 

 name. Persoon's Diderma when established, I.e., included 

 D. floriforme. He made some confusion 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 sporangial 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 



A. SUB-GENUS DIDERMA. 



1. Fructification wholly plasmodiocarpous . . . I. D. effusntn 



2. Fructification elongate and branching, but sometimes also distinctly 



interrupted, rounded, forming depressed isolated sporangia ; spores 



6-8 yu, . . . . . . . 2. D. reticulation 



Spores larger, 10-12 p . . . . . 3. D. persoonii 



3. Fructification of distinct sporangia. 



a. Sporangia on a common hypothallus. 



* Outer wall fragile, not widely remote from the inner, 



4. D. spumarioides 

 ** Outer wall crustaceous, porcelain-like. 



i. Spores 8-1 o /A 5. D. globositm 



ii. Spores 12-15 P- . 6. /?. crnstaceiim 

 *** Outer wall firm, not crustaceous . . . 7. D. lyallii 



