PHY S A RUM 79 



in the centre of each sporangium. In such cases the lime of the outer 

 peridium is scant or limited in amount, never forming the calcareous 

 cap shown in Fig. 1. The size of the spores is also variable. Rosta- 

 finski gives 12.5-14.2 /x; not infrequently a single spore reaches 16 /x, 

 a very unusual range of variation. 



The species is not common in the upper Mississippi valley, but 

 can be obtained in quantity where once it appears, as the plasmodia 

 are profuse. 



Ohio, Carolinas, Tennessee, Iowa, South Dakota, Kansas. Es- 

 pecially to be looked for on the bark of fallen stems of Populus and 

 Negundo. 



Brazil, India, Japan. 



Physarum lividum Rost., Alon., p. 95, is but a less calcareous form 

 of this, as is evident even by the author's description. Professor 

 Morgan thought P. lividum a phase of P. griseum Lk. Link, how- 

 ever, reckons P. griseum the same as P. cinereurii. Link, Diss., I., 

 p. 27. 



Physarum leucopus Link. 



Plate IX., Figs. 7,7 a, 7 b. 

 1809. Physarum leucopus Link, Diss., I, p. 27. 



Sporangia gregarious, stipitate, globose snow-white, with a didym- 

 ium like covering of calcareous particles ; stipe white, not long, conical 

 or tapering rapidly upward, slightly sulcate, brittle, from an evanes- 

 cent hypothallus ; columella none or small; capillitium, consisting of 

 rather long hyaline threads, connecting the usual calcareous nodes, 

 which are large, angular, snow-whitei; spore-mass black; spores by 

 transmitted light, violet-brown, distinctly warted, about 10 /t. 



The snow-white, nearly smooth stem, the small sporangium {yi 

 mm.) covered with loose calcareous granules, distinguish this rare 

 species. It looks like a small Didymium squamulosum. Fries called 

 it D. leucopus, Syst. Myc, III., p. 121. 



Rare. Iowa, Ohio Maine; Portugal. 



