100 ENDOSPORE^E. [DIDYMIUM. 



Physarunl Tussilaginis Berk. & Br., in Ann, Mag. Nat. Hist., 

 Ser. 4, xvii., p. 139. Didymium Tussilaginis Mass., Mon., p. 244. 



Plate XL., A. a. sporangia, stalked forms, x 20 ; b. sessile sporangia, 

 one is broken and shows the white columella, x 20 ; c. plasmodiocarp form 

 without columella, x 20 ; d. various forms of capillitium and spores, with 

 fragment of sporangium-wall, x 280 ; e. spore, x 600 (England). 



The varieties which, occur in this common species have led to different 

 forms receiving specific rank. Observations conducted for a length of 

 time on large growths among one heap of leaves show that the colour 

 of the capillitium varies from almost black to colourless in the same 

 locality ; a cluster on one leaf may present several shades, and even 

 in a single sporangium one-half of the capillitium may be dark and 

 the other half colourless ; this difference of colour is seen in all forms, 

 from the stalked sporangia to effused plasmodiocarps. The stalk and 

 columella may vary from white to bright orange. The characters given 

 as distinguishing D. squamulosum, D. macrospermum, D. discoideum, 

 D. prcBcox, and D. Fuckelianum are so inconstant that they cannot 

 be applied to mark even varieties of D. effusum. In the specimen 

 of D. effusum Host. (= D. confluens Rest., Mon., App., 22), in Strassb. 

 Herb., the sporangia are stalked or sessile, with delicate white capil- 

 litium. In the sporangium examined the threads in one portion are 

 without any thickenings ; in the remaining part there are numerous 

 small fusiform expansions apparently containing lime, as is not infre- 

 quent in this species ; the spores are minutely spinulose. The 

 specimen of D. macrospermum in Strassb. Herb, has colourless capillitium 

 springing from a large white columella ; the spores are strongly spinu- 

 lose, 10 to 11 ju, diam. ; the size of the columella in D. effusum is 

 very variable, and the large development in the Strassburg specimen 

 of D. macrospermum is by no means exceptional ; the roughness of the 

 spores is the only feature which deviates from the usual forms of 

 D. effusum, but as the spores of that species vary from nearly smooth 

 to spinose in the same heap of leaves, and present all intermediate 

 degrees of difference, this character cannot be taken as distinctive. 

 D. prwcox is described as having two walls ; the type specimen at 

 Strassburg is the frequent form of D. effusum, with the crust of 

 crystals on the sporangium- wall wrinkled and scaly, but the wall itself 

 is membranous and single. D. discoideum and D. Fuckelianum are 

 given as distinguished by the coloured stalk, columella, and capillitium, 

 and by the spotted sporangium- wall ; these characters are met with 

 in different degrees in sporangia of D. effusum, associated with 

 those having white stalks and those with colourless walls and capil- 

 litium. The type of D. radiatum Berk. & Curt. (K. 1516) is nearly 

 destroyed ; only the stalks remain, but these are characteristic of 

 D. effusum, being white and spreading at the base, deeply furrowed 

 and granular with deposits of lime ; Berkeley's description of the 

 capillitium and spores is not at variance with frequent forms of this 

 species. Chondrioderma Alexandrowiczii Rost., the type specimen of 

 which is in the Strassburg Herb., is probably a form of D. effusum ; 

 the sporangia are sessile, with the capillitium and spores of that species : 

 it differs from the type in the almost entire absence of lime. A 

 specimen from Lyrne Regis has the sporangium-wall similar to that 

 of the Strassburg specimen ; in both cases it is membranous with 

 cloudy spots of brown, and with calcareous deposits in the form of 

 scattered minute spicules ; the capiliitium in both is violet-brown, 

 beset with short spines, and colourless at the extremities ; the colu- 

 mella in both is represented by a brown thickening of the base without 



