124 Mycetozoa of North America 



Habitat: On dead wood, twigs, and leaves. 



Distribution: The typical form and var. minus are common 

 throughout North America; var. bicolor, *Bermuda, Kansas. 



Illustration: Lister, Mycetozoa ed. 3. pi. 112. 



This species produces large colonies, and is often found fruit- 

 ing in many developments at one time, usually in moist places. 

 In limestone regions the large, massive form, with heavy deposits 

 of lime, develops. The sporangia are often sessile, irregular in 

 shape, or confluent in groups. In areas without lime, the smaller, 

 neater var. minus is found. On Long Island, New York, where 

 lime is deficient in the soil, I have never found the typical form, 

 although var. minus is common. Intermediate forms, however, 

 are frequent, and have larger sporangia, stouter capillitia, and 

 larger spores. They connect the variety with the typical form. 

 Similar conditions may be observed in many other species of the 

 calcareous genera, and in those, as well as var. minus, the frail 

 forms cannot be regarded as distinct species. D. melanospermum 

 is very variable, particularly in the shape of the sporangia, the 

 quantity of lime present, the stalk, and the columella. Lime is 

 often present in the stalk. The specimens from Kansas regarded 

 as var. bicolor have stalks with lime throughout, but the wall of 

 the stalk is stained brownish. 



10. Didymium nigripes (Link) Fries, Syst. Myc. 3: 119. 1829. 

 Physarum nigripes Link, Ges. Nat. Fr. Berl. Mag. 3: 27. 1809. 



Plasmodium gray or colorless (Lister). Total height 1 to 

 1.5 mm. Sporangia gregarious, globose, umbilicate beneath, 

 0.4 to 0.7 mm. diam., stalked, erect, white; sporangial wall mem- 

 branous, clothed with white, stellate crystals of lime. Stalk 

 cylindrical, 0.6 to 1 mm. high, longitudinally striate, translucent, 

 dark brown, almost black. Columella small, often minute, glo- 

 bose, dark brown. Capillitium of delicate colorless or purplish 

 brown, branching threads. Spores pale violet-brown, faintly 

 warted or nearly smooth, 7-10 /x diam. 



Type locality: Europe. 



Habitat: On dead leaves and twigs. 



Distribution: Throughout North America. 



Illustration: Lister, Mycetozoa ed. 3. pi. 102, figs. a-c. 



This species, with D. eximium and D. xanthopus, forms a group 

 the members of which are distinguished mainly by the stalks 



