didymittm] didymiaceae 133 



The numerous varieties which occur in this common and widely 

 distributed 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 spinules on the spores are sometimes minute, 

 sometimes rather strongly developed, and are either regularly distributed 

 or grouped in a few large or small clusters. Spores showing small clusters 

 of rather larger spinules are of frequent occurrence in all forms of D. 

 squamulosum, and are found indeed occasionally in most species of 

 Didymium. The characters given as distinguishing D. effusum, D. 

 macrospermum, D. discoideum, D. praecox, and D. Fuckelianum are so 

 inconstant that they cannot be applied to mark even varieties of D. 

 squamulosum. In the specimen marked D. effusum Rost. in Strassb. 

 Herb., the sporangia are stalked or sessile, with slender 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 containing lime, an irregular development not 

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

 specimen of D. macrospermum in Strassb. Herb, has colourless capilli- 

 tium springing from a large white columella ; the spores are strongly 

 spinulose, 10 to 11/x diam. ; the size of the columella in the present 

 species is very variable, and the large development in the Strassburg 

 specimen of D. macrospermum is by no means exceptional. D. praecox 

 is described as having two walls ; the type specimen at Strassburg 

 is the frequent form of the present species, with the crust of crystals 

 on the sporangium-wall wrinkled and scaly. D. discoideum and D. 

 Fuckelianum are distinguished by the coloured stalk, columella, and 

 capillitium, and by the spotted membrane of the sporangium-wall ; 

 these characters are met with in different degrees in D. squamulosum, 

 associated with sporangia having white stalks and colourless walls and 

 capillitium. The type of D. radiatum Berk. & Curt, from Cuba 

 (K. 1516) is nearly destroyed; only the stalks remain, but these are 

 characteristic of the present species, being white, deeply furrowed, 

 granular with deposits of lime and arising from a discoid base. 

 Chondrioderma Alexandrowiczii Rost., the type specimen of which 

 from Poland is in the Strassburg Herb., is probably a form of D. 

 squamulosum ; the sporangia are sessile and have the capillitium and 

 spores of that species ; it differs from the typical form in the almost 

 entire absence of lime. A specimen from Lyme Regis has the spor- 

 angium-wall similar to that of the Polish specimen ; in both cases 

 it is membranous with cloudy brown spots, and with calcareous deposits 

 in the form of minute scattered spicules ; the capillitium in both is 

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

 the columella in both is represented by a brown thickening of the base 

 without lime deposits ; the points of difference are that in the 

 Polish specimen the sporangia are subglobose or of irregular shape 

 on a broad base, and the sporangium-wall is crumpled and whitish ; in 

 the Lyme Regis specimen the sporangium is a depressed plasmodiocarp, 

 and resembles a Lamproderma in the iridescent wall ; but it is associated 

 with other sporangia scantily furnished with lime, and also with 



