PHYSAEUM.] PHYSAEACEiE. 39 



e. Lime-knots white, sporangium grey or white — ■ 



Stalk straw-coloured, capillitium with a central ball 

 of lime. 17. P. nucleatum 



Stalk bufF, black, or white; sporangium subglobose ; 

 spores bright violet-brown. 19. P. nutcons 



Stalk black, buff, or white; sporangium laterally 

 compressed ; spores dark purple-brown. 



21. F. compressuni 

 Stalk red-brown, sporangium globose, white. 



20. P. calidris 

 Stalk white, membranous, sporangium ovoid. 



22. P. didermoides 



B. Sporangia sessile (never stalked) : — ; 



A., Lime-knots white— ^ 



a. Sporangium -wall single, spores pale violet-brown. 



23. P. cinereum 



b. Sporangium- wall double — 



a Sporangia scattered — 



Sporangia sinuous, murifoi-m, inner wall fragile. 



24. P. bivalve 

 Sporangia subglobose, or plasmodiocarps, inner 

 wall persistent. ' 25. P. Didei-ma 



ft Sporangia crowded — 



Sporangia reniform or subglobose, spores dark, 

 rough, 10 to 14 jj.. 26. P. contextum 



Sporangia angled by mutual pressure, spores pale, 

 nearly smooth, 8 to 10 /i. 27, P. conglomeratum 



B. Lime-knots red, or yellow-:— 



Lime-knots yellow, small, angular. 28. P. virescens 



Lime-knots red, large, angular. 30. P. rubiginosum 



Lime-knots yellow with red centre, rounded. 



29. P. iTicequale 



1. P. leucopus Link, Diss. I., p. 27 (1809). Plasmodium 

 opaque white. Total height about 1 mm. Sporangia globose, 

 cinereous, or glaucous, 0*5 mm. diam., gregarious, stipitate ; 

 sporangium-wall delicately membranous, containing scattered or 

 clustered, white, globular lime-granules. "Stalk white, stout, 

 0"15 to 0-2 mm. thick, with a few shallow longitudinal furrows, 

 erect, rigid, brittle, somewhat narrowing upwards, chalk-white 

 in section to the base, rising from a more or less developed white 

 hypothallus ; enclosing no refuse matter. Columella none, or 

 scarcely evident. Capillitium white, consisting of delicate, 

 branching, hyaline threads connecting the large irregular knots. 



