THE FUNGI WHICH CAUSE PLANT DISEASE 



303 



Son agglutinated 

 Spore-balls (variable) composed of 



thick-walled spores 10. Tolyposporella. 



Spore-balls with peripheral spores and 



central sterile cells 11. Testicularia. 



Of these genera numbers three to eleven inclusive occur on un- 

 important plants. Among them are: Polygonum, Rynchospora, 

 Psilocary, Cyperus, Carex, Luzula, Juncus, Fimbrystylis, Cissis; 

 various unimportant grasses, members of the Carduaceae, Faba- 

 ceae, Nyctaginacese, Amarantaceae, Cyperacese, Dracenaceae, and 

 Eriocaulacese. The most important genera are Ustilago and 

 Sphacelotbeca. 



Ustilago (Persoon) Roussel (p. 302) 



Sori on various parts of the hosts, at maturity forming dusty 

 spore masses, usually dark colored; spores single, produced irregu- 

 larly in the fertile mycelial threads which early entirely disappear 

 through gelatinization, small to medium in size; germination by 

 means of a septate promycelimn producing only infection-threads 

 or with sporidia formed terminally and laterally near the septa; 

 sporidia in water usually germinate into infection-threads but in 

 nutrient solutions multiply indefinitely, yeast- » 



fashion. 



About two hundred species, seventy-two of 

 which are given by Clinton ^ as occurring in 

 America. Besides the species discussed below 

 many others occurring upon grasses or other 

 plants of minor value are omitted. 



U. avenae (Pers.) Jens."' "«• "^' ''''• '^^ 



Sori in spikelets, rarely in leaves, forming a 

 dusty olive-brown spore-mass, about 6-12 mm. Fio. 2i9.— u. aye- 

 long by half as wide, usually rather completely in water. After 

 destroying floral parts, eventually becoming dissi- "* 

 pated; spores lighter colored on one side, subspherical to spherical 

 though often elongate, minutely echinulate, 5-9 n in length, 

 widespread on oats. 



The fungus was known by the name Ustilago as early as 1552 



