DIDYMWM 115 



Sturgis differs, as the name implies, principally in its greater com- 

 pactness and slightly smaller calcareous crystals; a desert phase. 



2. Didymium (Schrad.) Fr. 



1797. Didymium Schrad., Nov. Gen. Plant., p. 20, in part. 

 1829. Didymium (Schrad.) Fr., Syst. Myc, III., p. 113. 

 1875. Didymium (Schrad.) DeBy., Rost., Versuch, p. 13. 



Sporangia distinct, stipitate, sessile or even plasmodiocarpous, never 

 asthalioid ; the peridium thin, irregular in dehiscence, covered with a 

 more or less dense coating of calcareous crystals; columella more fre- 

 quently present; capillitium of delicate threads, simple or sparingly 

 branched, extending from the columella to the peridial wall. 



The genus Didymiurn, as set up by Schrader /. c, included a num- 

 ber of species now assigned to Diderma, Lepidoderma or Lamproder- 

 ma. Fries set out the didermas; DeBary and Rostafinski completed 

 the revision by setting out the remaining alien forms. 



The genus is among Myxomycetes instantly recognized by the 

 peculiar form of its calcareous deposits, stellate crystals coating, or 

 merely frosting, usually distinct sporangia. 



Key to the Species of Didymium 



1. Lime-crystals merely whitening the peridial wall. 



A. Fructification plasmodiocarpous. 



a. White. 



* Capillitium with adherent vesicles 1. D. complanatum 

 ** Capillitium simple . . . . 2. D. anellus 

 *** Capillitium much combined; spores 10-13 A^ 



3. D. luilczehii 

 **** Capillitium crystal-bearing . 18a. D. anomalum 



b. Yellow or tawny 4. D. fulvum 



B. Fructification normally of distinct sporangia. 



a. Sporangia sessile or nearly so; outer calcareous wall con- 



spicuously developed .... 5. Z?. crustaceum 



b. Sporangia plainly stipitate. 



i. Peridium much depressed; umbilicate below. 



* Stipe white . . . 6. D. squamulosum 

 ** Stipe black. 



t Larger, about 7.5-1 mm. 



7. D. mclanospermum 



ft Small, about .5 mm. . 8. D. minus 



ttt Sporangia discoid . 9. D. clavus 



