DICTYDJUM 231 



length umbilicate, stipitate, in color brown, or brownish purple; 

 the stipe varying much in length from two to ten times the diameter 

 of the sporangium, attaining 5-6 mm., generally erect, more or less 

 twisted and pallid at the apex, below dark brown, with hypothallus 

 small or none; calyculus often wanting, when present a mere film 

 connecting the ribs of the net ; the net made up chiefly of meridional 

 ribs connected at intervals by transverse parallel threads, above an 

 open Cribraria-Uke network closing the apex and more or less rudi- 

 mentary ; the spores varying in color through all shades of brown and 

 purple when seen in mass, by transmitted light reddish, 5-7 fi, smooth 

 or nearly so. 



This species in the United States is one of the most variable in 

 the whole group. The extremes of such variation might easily con- 

 stitute types for several distinct species were it not that in all direc- 

 tions the varieties shade into each other so completely as to defy 

 definition. We have before us specimens purple throughout and short- 

 stemmed ; purple with stem long, pale and twisted at apex ; brown, 

 with the same variations; short-stemmed, with the apex of the stem 

 pallid, and long-stemmed, with and without the same peculiarity. 

 Morgan (Cin. Soc. Nat. Hist. Jour., 1893) would set ofif the purple, 

 long-stemmed forms as D. longipes, "stipe three to five times the 

 sporangium," but here are forms in which the stem is ten times the 

 diameter of the sporangium, which yet possess in all other particulars 

 the characters of the short-stemmed forms. European forms also vary. 

 Massee figures one type ; Lister, one or two others ; Rostafinski's 

 figure indicates a taller form; Fries says, "Stipes elongatus, peridio 

 quinquies et ultra longior." It seems reasonable to suppose that 

 the variation is largely due to atmospheric conditions at the time of 

 fruiting. The purple forms may be cases of arrested development, 

 since the plasmodium appears to be in all cases purple, or at least 

 they seem to represent those plasmodia which have failed of normal 

 ripening. We may recognize two or three general types, distingin'shed 

 primarily by color: — 



a. D. cancellatum cancellatum. — Sporangia clear brown or with 

 only a purplish tinge, the stipe tapering upward, and in ex- 

 treme cases perfectly white at the twisted apex. The stipe in length 

 ranges from three to ten times the diameter of the sporangium. The 



