26 THE NORTH AMERICAN SLIME-MOULDS 



Key to the Species of Physarum. 



A. Fructification asthalioid . . . . i. P. ellipsosporum 



B. Fructification plasmodiocarpous. 



a. White 2. P. sinuosuut 



b. Yellow 3. P. serptila 



c. Gray, forms of 19. P. nefroidcuin 



C. Fructification of distinct sporangia. 



a. Sporangia in typical forms sessile. 



i. Peridium red or red brown. 



* Peridium simple . . . . 8. P. later it inm 

 ** Peridium double, with red flakes, 37. P. rubiginosum 



*** Peridium double, smooth . . 7. P. brunneoluin 



ii. Peridium yellow or ochraceous. 



* Peridium simple. 



f Sporangia minute, crowded spore-mass, purple, 



12. P. thejoteum 



ft Sporangia sessile clustered, greenish . 9. P. virescens 

 ** Peridium double. 



f Outer peridium reflexed . . 6. P. conglomeratum 

 ff Outer peridium not reflexed . . 5. P. context urn 

 iii. Peridium ashen or gray. 



* Peridia aggregated in heaps . . 13. P. air inn 

 ** Peridia minute, scattered . . u. P.plitmbeiim 



*** Peridia larger, peridia gray . . . 10. P. cinereiun 

 iv. Peridium white and double . . 4. P. diderma 



b. Sporangia, in typical forms, stalked. 



i. Stipe generally short, less than the diameter of the sporan- 

 gium. 



* Fructification purple . . . 14. P. newtoni 

 ** Fructification straw-colored . 15. P. catspitosinn 



*** Fructification gray, calcareous ; stalk pale to fuscous, 



forms of 19. P. nefroidenm 



**** Sporangia blue gray, sometimes capped with lime ; stalk 

 pure white when present, often scanty, weak, 



1 8. P. didermoides 

 ii. Stipe longer, greater than the diameter of the sporangium. 



* Stipe calcareous, white. 

 \ Columella none. 



1. Sporangium white, stipe unfluted, 26. P. leucopus 



2. Sporangium white, stipe channelled, formS of, 



19. P. nefroideum 

 ft Columella evident. 



1. Sporangium white . . 23. P. globulifermn 



2. Sporangium yellow . . 25. P. inelleuin 

 ** Stipe calcareous, not white. 



