physarttm] physaraceae 41 



opaque with deposits of lime in the wall- substance ; or the 

 tube may be filled at the base or throughout with refuse 

 matter discharged from the plasmodium, or with deposits 

 of lime, giving the stalk a brittle structure with a chalk-like 

 section. CapiUitium forming a network of hyaline threads 

 with vesicular expansions containing deposits of lime (lime- 

 knots). 



The genus Tilmadoche is described by Rostafinski (Mon., p. 126) a3 

 differing from Physarum in the capillitium forking repeatedly at a 

 narrow angle, and being provided with few and small lime-knots. 

 These characters are too inconstant to be of value in classification. 

 In P. nutans Pers., which from its abundance affords ample facility 

 for study, we not infrequently observe in a growth from one plasmodium 

 some sporangia with capillitium characteristic of Physarum and others 

 of Tilmadoche. P. polycephalum Schwein. (syn. T. gyrocephala Rost.) 

 frequently has capillitium with large lime-knots and broad membranous 

 expansions. T. oblonga Rost. and T. Mans Rost. are now included 

 under Physarella oblonga (Berk. &Curt.) Morgan, a species distinguished 

 from its allies by well-marked characters of shape and capillitium that 

 fully entitle it to a position in a separate genus. For these reasons 

 the genus Tilmadoche is not retained. 



KEY TO THE SPECIES OF PHYSARUM. 



. Sporangia stalked (occasional sessile forms) :— 

 a. Stalks charged with lime throughout — 



a. Capillitium lax — 



Stalk white ; sporangia grey ; lime-knots large, white ; 

 columella none. 1. P. leucopus 



Stalk white, rarely rufous ; sporangia tawny, 

 globose; columella conical. 2. P. melleum 



Stalk white ; sporangia sulphur-yellow ; columella 

 none. 3. P. sulphureum 



Stalk olive or yellowish, short or absent ; sporangia 

 olive or yellow, globose, ovoid or forming plas- 

 modiocarps; columella none. 4. P. variabile 



Stalk and sporangium yellow or orange ; columella 

 large, hemispherical. 5. P. luteo-album 



b. Capillitium dense, persistent — 



Stalk white or brownish below ; sporangium white ; 

 lime-knots small, white. 6. P. globuliferum 



Stalk, sporangium, and lime-knots red. 



7. P. pulchripes 



Stalk, sporangium, and lime-knots mouse-brown. 



8. P. murinum 



