110 THE MYXOMYCETES 



8. DlDYMIUM CRUSTACEUM Fr. 



Syst. Myc. 3 : 124. 1829. 

 PL VIII, Fig. 176. 



1875. Didymium confluens (Pers.) Rost., Mon. 164. 



Sporangia closely aggregated, globose, or by compression deformed, 

 sessile, snow-white by virtue of the remarkably developed covering 

 of calcareous crystals by which each sporangium is surrounded as if 

 to form a crust; peridium membranous, colorless, usually shrunken 

 above and depressed; columella pale, small, or obsolete; hypothallus 

 scant or vanishing; capillitium of rather stout violaceous threads 

 seldom branched except at the tips, where they are pale and often 

 bifid, or more than once dichotomously divided; spores strongly warted, 

 globose, violet-brown, 10-13 /jl. 



This species has in some ways all the outward seeming of a diderma, 

 but cannot be referred to that genus because of the crystalline char- 

 acter of its crust. This is a very marked structure; loosely built up of 

 very large crystals, it is necessarily extremely frail, nevertheless per- 

 sists, arching over at a considerable distance above the peridium 

 proper. Sometimes, however, caducous, evanescent. 



The sporangia are said to be sometimes stipitate. This feature 

 does not appear in any of the material before us. The hypothallus 

 is sometimes noticeable under some of the sporangia where closely 

 crowded, but is not a constant feature. 



Rostafinski (Mon. 164) seems to have confused this species with 

 Persoon's Physarum confluens. In the Appendix he substitutes the 

 Friesian nomenclature. Persoon's description of his species is insuffi- 

 cient, and throws no light on the problem whatever. 



Rare. Canada, Iowa, South Dakota, Colorado, Washington, Bolivia; 

 Europe, Japan. 



9. Didymium intermedium Schroeter 



Hedwigia 35 : 209. 1896. 

 1902. Didymium excelsum Jahn, Ber. Deutsch. Bot. Ges. 20 : 275. 



Sporangia clustered or gregarious, discoidal and umbilicate be- 

 low, or lobed or convolute, grayish white, stipitate; stipe pale yellow, 

 tapering upwards, stuffed with lime crystals, expanding into the yel- 

 lowish, discoidal, recurving columella; capillitium colorless, more or 

 less branching; spores dark purple-brown, irregularly reticulate, 9-12 ji. 



Differs from D. squamulosum mainly in the reticulate epispore and 

 the structure of the stalk. A collection from southern California 

 (O. A. Plunkett 178) determined as this species by Miss Lister, has 



