Stemonitis 141 



ing threads of the capillitium take their origin. In this family 

 the more or less solid stalk is developed within the young, rising 

 sporangium. 



Sporangial wall evanescent; capillitium springing from 



all parts of the elongate columella, the ultimate branch- 

 lets united to form a surface-net. 

 Sporangial wall evanescent; capillitium as in Stemonitis, 



but not forming a surface-net, or onK- imperfectly 



towards the base. 

 Sporangial wall evanescent; columella reaching to the 



apex of the sporangium, and there expanding to a 



circular disc from which the capillitium is suspended. 

 Sporangial wall more or less persistent as an iridescent 



membrane; capillitium radiating from the columella. 

 Sporangial wall persistent in the form of small discs at 



the tips of the rigid, forking threads of the capillitium; 



columella short or hardi}' evident. 

 Capillitium scanty, colorless, branching from a short 



columella; sporangia very small. 

 Sporangia minute, stalked, brown; capillitium absent. 



Genus 16. STEMONITIS Gleditsch, Meth. Fung. 140. 

 1753. 



Sporangia cylindrical, stalked, distinct or fasciculate; stalk 

 solid, black, extending to near the apex as a columella, except in 

 confluent forms; capillitium composed of numerous threads ra- 

 diating from all parts of the columella and combined into a loose 

 network, the ultimate branches united into a surface-net, often 

 incomplete in irregular developments. 



Type species: Stemonitis fusca Roth. 



Several members of the genus are susceptible to drying condi- 

 tions prevalent during the period of sporangial formation. If the 

 habitat is exposed to the sun, or to strong winds, or the air is so 

 dry that drying proceeds too rapidly, erratic forms may be pro- 

 duced. The differences appear as wide divergence in the sizes 

 of the meshes of the surface-net, or its partial or entire absence; 

 weakness or irregularity in the capillitium or stalk; or partly con- 

 fluent sporangia. Some of these forms approach the genus 

 Comatricha, and others the genus Amaurochaete, and have been 

 erroneously considered as distinct species. As conditions vary 

 the forms will vary, so that few are comparatively alike. In most 

 instances relationship to a particular species of Stemonitis may be 

 established by the characters of the spores. While not true varie- 



