Didymium. 219 



capillitium usually well-developed, threads thin, without lime, 

 coloured or colourless, either radiating from the columella or 

 base of sporangium as simple or furcate threads, which usually 

 combine laterally towards the apex, or combine throughout 

 their length to form a dense, irregular network, with the angles 

 more or less triangular and flattened. Spores lilac or violet- 

 brown. 



Didymium, Schrad., Nov. pi. gen., p. 20. Host, Mon., p. 160 

 (in part) ; Cooke, Myx. Brit., p. 30 (in part) ; Sacc., Syll., v., 7, 

 pt. I., p. 376 (in part) ; Zopf, p. 150. 



The leading idea of the genus as defined above is, the wall 

 of the sporangium with lime outside, the thin threads of the 

 capillitium not containing lime, either radiating, subsimple or 

 bifurcating, or anastomosing irregularly throughout their length 

 and forming a net as in the subgenus Hcmididymium, the 

 species of which are distinguished from those of Tilmadoche 

 by the absence of well-defined, small, usually fusiform knots 

 containing granules of lime. Thickenings are not uncommon 

 in the capillitium of various species of Didymium, but lime is 

 never present. 



Distrib. Temperate and tropical regions. Species 50. 



Sub-Gen. Didymium. 



Threads of capillitium almost simple, or bifurcating at acute 

 angles, here and there connected laterally, but not forming a 

 uniform net throughout the capillitium. 



A. Sporangium stipitate. 

 (Sessile forms occur in D. squamulosum and D. farinaceum.) 



* Spores warted. 



Didymium farinaceum, Schrad. (figs. 2935). t meWo^ww 1 



Sporangium hemispherical, usually a little depressed, more 

 or less umbilicate below, at first white with a continuous crust 

 of lime, which soon becomes broken up into white glistening 

 granules scattered on the inner dark, wrinkled wall ; stem 



