126 Mycetozoa of North America 



darker and rougher than those of the related species. It is 

 possible that D. megalosporum Berk. & Curt, represents the 

 present species, and if so, the name would take precedence. 



12. Didymium xanthopus (Ditm.) Fries, Syst. Myc. 3: 120. 

 1829. 



Cionium xanthopus Ditm. in Sturm, Deutsch. Fl. Pilze 1: 87. 1816. 

 Didymium tiigripes (Link) Fries var. xanthopus (Ditm.) Lister, Mycetozoa 98. 

 1894. 



Plasmodium? Total height 1 to 1.5 mm. Sporangia gre- 

 garious, globose, umbilicate beneath, 0.4 to 0.8 mm. diam., 

 stalked, erect, white; sporangial wall membranous, clothed with 

 white, stellate crystals of lime. Stalk cylindrical, longitudinally 

 striate, 0.6 to 1 mm. high, translucent, reddish brown, not dark. 

 Columella white or pale, globose, subglobose, or turbinate. 

 Capillitium of delicate, colorless or purplish brown, branching 

 threads. Spores pale violet-brown, faintly warted or nearly 

 smooth, 7-10 /i diam. 



Type locality: Germany. 



Habitat: On dead leaves, mosses, and twigs. 



Distribution: Common and abundant throughout North 

 America. 



Illustration: Lister, Mycetozoa ed. 3. pi. 102, figs, e-g, as 

 D. nigripes var. xanthopus. 



This species is very prolific, with a short life-cycle from germi- 

 nation of the spores to maturity of the fruit, and with many 

 broods, so that under favorable conditions it will be found de- 

 veloping continuously in great abundance throughout the season. 

 It is rarely found in dry areas, and prefers those parts of swamps 

 and marshes where the water flows or seeps away, leaving the 

 substratum moist. In the swamps of Long Island, New York, 

 I have often observed hundreds of large developments in a single 

 day, but D. nigripes has only been found four times, and D. 

 eximium but once, over a period of twenty years. Contrariwise, 

 the two latter species have been collected frequently each season 

 in dry, inland regions. D. xanthopus is distinguished from D. 

 nigripes by the reddish brown stalk and pale columella. 



Somewhat reluctantly, the three foregoing forms are treated 

 as distinct species. There are occasional intermediates, and 

 they seem to form when dry or moist conditions of habitat are 

 reversed. The forms are very constant in nearly all collections 



