DIDYMIUM 105 



dictyospora described by R. E. Fries (Arkiv for Botanik 1 : 66) differs 

 from the type chiefly in its finer capillitial threads and its darker spores 

 with longer spines and fine reticulate sculpture; the other from Colo- 

 rado, var. solida Sturgis (= Spumaria solida Jahn) differs, as the name 

 implies, principally in its greater compactness and slightly smaller 

 calcareous crystals; a desert phase. 



Common in the United States, especially east of the Rockies, South 

 America; Europe, Africa, Australia. 



2. Didymium Schrad. emend. Fries 

 Syst. Myc. 3 : 113. 1829. 

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



Sporangia distinct, stipitate, sessile or even plasmodiocarpous, never 

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

 or less dense coating of calcareous crystals; columella more frequently 

 present; capillitium of delicate threads, simple or sparingly branched, 

 extending from the columella to the peridial wall. 



The genus Didymium, as set up by Schrader, included a number of 

 species now assigned to Diderma, Lepidoderma or Lamproderma. 

 Fries set out the didermas; de Bary and Rostafinski completed the re- 

 vision by removing the remaining alien forms. 



The genus is instantly recognized by the peculiar form of its cal- 

 careous deposits, stellate crystals coating, or merely frosting, usually 

 distinct sporangia. 



KEY TO THE SPECIES OF DIDYMIUM 



a. Lime crystals aggregated into discoidal, often concave 



scales, sessile or plasmodiocarpous I. D. nivicolum 



a. Lime crystals scattered or forming a powdery coating 



on surface of peridium ° 



a. Crystals combined to form a shell-like crust * 



b. Plasmodiocarpous c 



b. Sporangiate / 



c. Yellowish or tawny; spores dark, tuberculate, 12-15 fj. 2. D.fulvum 



c. Pale brown or ochraceous; spores pale, smooth, 5-7 /x 3. D. ochroideum 



c. Lime coat white; inner peridium usually dark » 



d. Flattened, thin; capillitium bearing conspicuous 



vesicles 4. D. complanatum 



d. Capillitium not bearing vesicles e 



e. Capillitium of vertical, tubular columns containing 



crystalline lime 5. D. anomalum 



e. Capillitium only slightly branched; columella lacking; 

 plasmodiocarps small; sometimes sporangiate, rarely 

 with a short stalk 6. D. anellus 



