116 



Mycetozoa of North America 



Lime-crystals stellate; sporangia simple. 



Lime-crystals stellate, heaped together, at first concealing 



the confluent sporangia. 

 Lime-crystals more or less lenticular and scale-like, thickly 



scattered over the sporangial wall. 

 Lime-crystals few, minute, flat, sometimes absent. 



11. DiDYMIUM 



12. mucilago 



13. Lepidoderma 



14. Leptoderma 



Genus 11. DIDYMIUM Schrader, Nov. Gen. PI. 20. 1797. 



Sporangia stalked, sessile, or forming plasmodiocarps; spo- 

 rangia! wall membranous or cartilaginous, with superficial crys- 

 tals of lime either scattered over the surface or combined into a 

 separable crust. Capillitium of branching threads, which are 

 thickened at intervals with dark calyciform nodes, in normal 

 developments without lime-knots, in D. Sturgisii consisting of 

 simple tubes containing lime-crystals. 



Type species: Didymium farinaceum Schrad. 



Crystals closely combined to form a thin, eggshell- 

 like crust. 

 Sporangia or plasmodiocarps alwaj's sessile, white 

 or gray. 

 .Sporangia pulvinate; capillitial threads scanty, 

 broad at the base, or profuse and slender 

 throughout; spores nearly smooth. 

 Sporangia pulvinate; capillitium a network of 

 stout, purple threads; spores rough with 

 close-set warts and ridges. 

 Sporangia pulvinate or branching plasmodio- 

 carps; spores rough with short spines. 

 Sporangia flat or convex; capillitium dark, 

 profuse, slender at the points of attachment. 

 Sporangia short-stalked or sessile, turbinate, white 

 or cream-colored; capillitium rigid, usually 

 colorless. 

 Crystals scattered or loosely combined into a crust. 

 Sporangia and plasmodiocarps always sessile (ex- 

 cept in D. fidvum). 

 Plasmodiocarps white or gray; capillitium with 

 large, vesicular spore-like bodies. 

 Plasmodiocarps depressed, flattened or ef- 

 fused; columella absent. 

 Plasmodiocarps branched and netted, lat- 

 erally compressed; columella a thin, 

 vertical plate. 

 Sporangia or plasmodiocarps without vesicu- 

 lar bodies. 



1. D. difforme 



2. D. quitense 



3. D. trachysporum 



4. D. Lisleri 



5. D. vaccinum 



6. 



7. 



D. complanatum 

 D. parietale 



