PHYSARUM 41 



however, had certain advantages of convenience. One possible solu- 

 tion seems to be to treat the genus Physarum as a whole, but to 

 segregate the species into two sections, Euphysarum and Tilmadoche. 

 In using the key, it should be borne in mind that a number of 

 sessile species may be somewhat plasmodiocarpous in some collec- 

 tions, and that stipitate species may be sessile at times. For the pur- 

 poses of the key, each species is placed under what is believed to be 

 its more representative expression. 



KEY TO THE SPECIES OF PHYSARUM 



Capillitium irregularly reticulate; lime-knots various, 



typically large and irregular I. Section Euphysarum 



Capillitium regular, forked and radiating; lime-knots 



smaller, fusiform II. Section Tilmadoche 



I. Euphysarum 



a. Fructification sessile, often plasmodiocarpous b 



a. Fructification sporangiate, stalked I 



b. Peridium single, or, if double, inner peridium very delicate and closely 



attached to outer c 



b. Peridium plainly double h 



c. White or cinereous d 



c. Some shade of yellow or green e 



c. Orange-red, red or brown / 



c. Dark gray, dull violet, blue or iridescent g 



d. Peridium granular; spores sometimes oval 1. P. ovisporum 



d. White or gray, calcareous; spores dark, rough, 9-12 it 2. P. vernum 

 d. Cinereous; wall thin, delicate; spores bright lilac, 



finely spinulose, 7—11 yu, 3. P. cinereum 



d. Sessile, but narrowed at base; lime forming a fine 



reticulation over surface 4. P. gilkeyanwm 



d. Sporangia depressed, annulate or umbilicate above, 



rarely with short stalks; spores 12-15 /x 5. P. megalosporum 



d. Gray, sometimes slightly bluish; peridium smooth; 



spores pale, 6-8 /x 6. P. sessile 



e. Pale yellow to ochraceous; spores 10-13 // 7. P. serpula 



e. Bright yellow; spores 9-12 y. 8. P. aureum 



e. Yellow or greenish yellow to green; spores 7-10 /x 9. P. virescens 



f. Vermilion or scarlet; lime-knots rounded, yellow, often 



with red centers 10. P. lateritium 



f. Rusty or reddish brown; lime-knots angular, dull red 



or yellowish 11. P. rubiginosum 



f. Tawny or clay colored; very small, crowded; spores 



6-7 fj, 12. P. digitatum 



f. Brownish orange or chestnut; spores 10-12 /z 13. P. famintzini 



■.,. Dull violet-brown; small, densely clustered and super- 

 imposed 14. P. confertum 



;. Blue-gray, iridescent; lime in form of flat scales 15. P. lepidoideum 



