256 THE LOWER FUNGI— PHYCOMYCETES 



2. Thamnidium Link (Berl. Mag. Naturf. Freunde, 3: 31, 1809). 



syn. Ilelicostylum Corda p, p. (Icon. Fung., 5: 18, 55, 1842). 



Bulbothamnidium Klein p. p. (1870: 557). 



Chaetostylum van Tieghem & le Monnier p. p. (1873: 



328). 



Sporangiophore erect, consisting of a cylindrical central axis, 



usually terminated by a single, large, many-spored sporangium, 



and lateral branches bearing numerous, small, few-spored 



sporangiola (Fig. 90); lateral branches usually several times 



divided; the ultimate branchlets straight or circinate, terminating 



in sporangiola, or tapering into sterile spines; sporangium 



provided with a prominent columella; sporangiolum lacking a 



columella, containing one to twenty or more (usually about four) 



spores; spores alike in both sorts of sporangia; zygospores as 



far as known formed as in Mucor from approximately equal 



gametangia. 



Individual sporangiophores, bearing only sporangiola, and 

 others, bearing only the terminal sporangium, are not infrequently 

 encountered. Three subgenera are recognized here. 



Subgenus Euthamnidium Schroter (1893: 127). 



Lateral branches of the sporangiophore typically dichoto- 

 mously branched, the ultimate branchlets not circinate and 

 usually all bearing sporangiola. About a half dozen species are 

 included here, of which the best known is Th. elegans Link. 



Subgenus Chaetostylum (van Tieghem & le Monnier) Schroter. 

 syn. Bulbothamnidium Klein (1870: 557). 

 Lateral branches of the sporangiophore verticillately branched, 

 the central axis of each successive division swollen at the point 

 of origin of the whorl of branches, and prolonged beyond them 

 into a sterile spine. Two or three species are placed here, 

 including Th. fresenii (van Tiegh. & le Monn.) Schroter, the 

 type of this group. (See Sumstine, 1910: 143). 



Subgenus Helicostylum (Corda) Schroter. 



Lateral branches of the sporangiophore monopodially or 

 cymosely branched, the ultimate branches circinate; in some cases 

 the central axis terminating in a spine as in the preceding sub- 

 genus. The species Th. amoenum (Preuss) Schroter [Ilelicosty- 

 lum elegans Corda] and about a half dozen other species fall here. 



