DIDYMIUM 125 



Since, however, they are the usual presentation of the species in the 

 United States, it seems wise to let them stand for the present, as here. 

 They are quite distinguishable; D. eximium especially well marked. 

 Apparently rare, it yet ranges from New York to eastern Iowa, in 

 colonies rather large. Okoboji Lake; — fine! 



13. DiDYMIUM TROCHUS LtSt. 



1898. Didymium trochus List., Jour. Bot., XXXVI., p. 164. 



Sporangia plasmodiocarpous, hemispherical or turbinate, white, ses- 

 sile or very short-stalked, cream-colored or white; peridium double, 

 the outer shell-like, the inner membranaceous, more or less adherent 

 to the outer, both caducous together, leaving the thickened base sur- 

 rounding an expanded columella; stipe, when present, very short, 

 stout; capillitium colorless, nearly simple; spores brownish-purple, 

 strongly warted, 9-10 /a. 



On decaying leaves, rotten cactus, yucca, etc., Monrovia, Cali- 

 fornia; Bethel. 



Reported from England on beds of leaves or straw; in Portugal 

 Dr. Torrend finds it on or in dead leaves of Agave americana! Evi- 

 dently an American species, and belonging to arid regions; its occur- 

 rence in England surprising! 



14. Didymium annulatum Machr. n. s. 



Plate XX,, Figs. 4, 4 a. 



Sporangia small, scattered, annulate, not only without columella 

 but perforate when the stipe is broken, umbilicate above and below, 

 grey, coated with crystalline frustules, opening irregularly about the 

 periphery ; stipe white, or pallid, fluted, tapering upward from a dis- 

 tinct hyp>othalIus ; capillitium scanty consisting of delicate, sparsely 

 branching threads, the branchlets anastomosing more or less at length, 

 attached to the peridial wall, radiating from the rim of the slightly 

 depressed top of stipe, without special thickenings save at the inser- 

 tion of the ramules a triangular enlargement is usual and of dark or 

 pallid shade; spores smooth; however they show three or four spots 



