96 Mycetozoa of North America 



ignore these variations in form by combining them in a broadened 

 description. This policy has been followed in many species and 

 should be extended. D. effusum is closely related to D. hemi- 

 sphericum and to D. testaceum, and connecting forms are not rare. 

 From D. testaceum it is distinguished by the more frequent plasmo- 

 diocarpous habit, the more flattened sporangia, the form of the 

 columella, and the absence of the pinkish color. Occasionally 

 the sporangia may be dotted Avith vitreous plates as in the genus 

 Lepidoderma. 



4. Diderma Chondrioderma (de Bary & Rost.) G. Lister, Myce- 

 tozoa ed. 3. 258. 1925. 



Didymium Chondrioderma de Bary & Rost.; Alex. Stro. Miksom. 89. 1872. 



Chondrioderma Alexandroiviczii Rost. Mon. 169. 1874. 



Diderma arboreum G. Lister & Fetch; G. Lister, Jour. Bot. 51: 2. 1913. 



Plasmodium? Sporangia scattered, discoid, sessile, rarely 

 stalked, 0.5 to 0.7 mm. diam., or forming expanded and lobed, 

 flattened plasmodiocarps 1 to 3 mm. diam., white or purplish gray 

 from absence of lime; sporangial wall membranous, with deposits 

 of round or angular lime-granules, either united to form a thin 

 crust or sparsely distributed, often with scattered deposits of 

 refuse matter. Stalk when present very short, dark brown. 

 Columella low, convex, flesh-colored, or reduced to a slight thick- 

 ening of the sporangium-floor, with deposits of lime in the form 

 of granules or small nodules, often mixed with refuse matter. 

 Capillitium consisting of simple or branching and anastomosing, 

 colorless or purplish, rather stout threads, often with membranous 

 expansions at the axils. Spores very minutely and closely spin- 

 ulose, pale purplish gray, 10-15 n diam. 



Type locality: Poland. 



Habitat: On bark of dead and living trees, mosses, and lichens. 



Distribution: California, *Iowa. 



Illustration : Lister, Mycetozoa ed. 3. pi. 206, as D. arboreum. 



The California collection made by Miss E. E. Morse is typical. 

 The sporangia and plasmodiocarps are scattered on wood, and 

 have scanty lime interspersed by deposits of dark refuse matter. 

 The capillitium consists of coarse threads, and the spores are pale, 

 measuring 1 1-12 n diam. The species is allied to D. effusum, and 

 resembles the latter superficially, but is distinguished by the 

 larger spores and coarser threads of the capillitium. 



