DIDYMIUM.] DIDYMIACE-E. 



Order II. DIDYMIACE.E. Deposits of lime in crystals or 

 crystalline discs distributed over the sporangium-wall ; capillitium 

 without lime-knots; sporangia simple, except in Spv.ma.Tia, where 

 they are combined into an sethalium. 



KEY TO THE GENERA OF DIDYMIACE^E. 



Lime-crystals stellate, distributed over the sporangium -wall. 



(12) DIDYMIUM. 



Fig. 20. Didymium cffusum Link. 



a. Two sporangia, one entire, the other showing 



columella and capillitium. Magnified 12 

 times. 



b. Capillitium and fragment of sporangium- 



wall, with crystals of calcium carbonate 

 and two spores. Magnified 200 times. 



Fig. 20. 



Lime-crystals heaped together, at first concealing the confluent 

 hollow sporangia. 



(13) SPUMARIA. 



Fig. 21. Spumaria alba DC. 



a. ^thalium. Natural size. 



b. Capillitium and fragment of sporangium-wall, 



with crystals of calcium carbonate and 

 two spores. Magnified 200 times. 



a 



Fig. 21. 



Lime-crystals lenticular, marked with radiating strire, scattered 

 over the sporangium- wall. 



(14) LEPIDODERMA. 



Fig. 22. Lepidodevma tiyrinum Host. 



a. Sporangium. Magnified 6 times. 



b. Capillitium and spores. Magnified 140 times. 



Fig. 22. 



Genus 12. DIDYMIUM Schrader, Nov. Gen. Plant., p. 20 

 (1797). Sporangia stalked, sessile, or plasmodiocarps, not 

 forming an sethalium ; sporangium-wall membranous, beset with 



