94 ENDOSPORE^E. [DIDYMIUM. 



superficial crystals of lime either scattered over the surface or 

 combined into a separable crust ; capillitium of branching threads, 

 which are often thickened at intervals with dark calyciform 

 nodes, without lime-knots. 



KEY TO THE SPECIES OF DIDYMIUM. 



A. Superficial crystals closely combined to form a thin shell-like 



crust : 

 Capillitium scanty, usually broad at the base. 



1. D. diffbrme 

 Capillitium profuse, slender at the extremities. 



2. D. dubium 



B. Superficial crystals scattered or loosely combined :- 



A. Plasmodiocarps, capillitium associated with large, olive- 



coloured vesicles. 3. D. Serpula 



B. Sporangia usually stalked, capillitium without large 



vesicles 



a. Sporangia disc-shaped, columella absent. 4. D. Clavus 



b. Sporangia subglobose 



Stalk and columella dark brown, stalk opaque and 

 granular. 5. D . farinaceum 



Stalk olive-brown or orange, hornclear. 



6. D. nigripes 



Stalk and columella white ; crystals on sporangium- 

 . wall scattered or forming a wrinkled crust. 



7. D. effusum 



Coltimella nearly white, stalk when present mem- 

 branous ; crystals on sporangium-wall forming 

 a smooth, thick, deciduous envelope enclosing the 

 pale membranous stalk. 8. D. crustaceum 



1. D. difforme Duby, Bot. Gall.,ii.,p. 858 (1830). Plasmodium 

 colourless or pale yellow. Sporangia pulvinate en a broad base 

 or irregularly elongated and forming plasmodiocarps, scattered, 

 0-4 to 2 mm. or more long, smooth, white ; sporangium-wall of 

 two layers, the outer a thin crust of densely combined minute 

 crystals of lime, separating from the iridescent membranous 

 inner layer, which is purplish or nearly colourless above, stout 

 and yellowish-brown at the base, thickened at the margin. 

 Columella none. Capillitium often very scanty, of coarse or 

 delicate, purple or colourless, flattened threads, usually broad at 

 the base, branching dichotomously and slender above. Spores 

 dark purple-brown, faintly warted, 11 to 14 /JL diam. Diderma 

 diffbrme Pers., Disp. Meth., p. 9 (1797). Chondrioderma diffbrme 

 Rost., in Fuckel, Symb., Nachtr., p. 73; Mon., p. 177; Cooke, 

 Myx. Brit., p. 39 ; Lister, in Ann. Bot., vol. iv., No. xiv., p. 282 



