didymium] 



DIDYMIACEAEj 



123 



Lime-crystals more or less lenticular and marked with radiating 

 striae, scattered over the sporangium-wall. 



(17) Lepidoderma. 



Fig. 25. — Lepidoderma tigrinum Rost. 

 o. Sporangium. Magnified 6 times. 

 b. Capillitium and spores. Magnified 140 times. 



Fig. 25. 



Genus 15.— DIDYMIUM Schrader 1 No v. Gen. Plant., 20 

 (1797). Sporangia stalked, sessile, or forming plasmodiocarps, 

 not united into an aethalium ; sporangium-wall membranous 

 or cartilaginous, beset with 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. 



The subgenus Lepidodermopsis forms a connecting link between the 

 true Didymia and the genus Lepidoderma, having the superficial 

 stellate crystals of the former, and the cartilaginous sporangium- wall 

 of the latter. 



KEY TO THE SPECIES OF DIDYMIUM. 

 Subgenus 1. — Eudidymium. Sporangium-wall mem- 

 branous. 



A. Superficial crystals closely combined to form a thin egg- 



shell-like crust : — 



Sporangia sessile, pulvinate ; capillitium threads 

 scanty, broad at the base or profuse and slender 

 throughout ; spores usually smooth. 



1. D. difforme 



Sporangia sessile, pulvinate; capillitium a network 

 of stout purple threads ; spores rough. 



2. D. quitense 



Sporangia sessile, flat ; capillitium rigid, dark, 

 profuse, slender at the points of attachment. 



3. D. dvhium 



Sporangia turbinate, shortly stalked or sessile ; 

 capilhtium rigid, usually colourless. 4. D. Trochus 



B. Superficial crystals scattered or loosely combined : — 



a. Plasmodiocarps ; capillitium associated with large olive- 

 coloured vesicles. 5. D. complanatum 



