318 



THE FUNGI WHICH CAUSE PLANT DISEASE 



Urocystis Rabenhorst "' (p. 314) 



Sori usually in the leaves or stems, occasionally in other parts, 

 producing dark-colored, usually dusty, spore-masses; 

 spore-balls permanent, composed of an enveloping 

 cortex of tinted sterile cells and usually one to 

 Fig. 233.— Spore several interior fertile cells; fertile cells generally 



balls of U. ce- , , , , . , . . , , 



puia5. After dark-colored ; germmation often by a short promyce- 

 Thaxter. jj^^^ ^^^^^ ^^.^ 



duces terminally-grouped spori- 

 dia; these give rise to similar 

 secondary sporidia or to infec- 

 tion-threads. 



Besides the forms discussed 

 below, foreign species are listed 

 on Anemone, Liliacese, Gladiolus, 

 Primula, etc. 



U. cepulae Frost.^'' ^ "»' i^« 



Sori in leaves, forming isolated 

 pustules or affecting them for 

 the greater part of their length 

 and breadth, sometimes occur- 

 ring at their bases, in the bulbs. 

 Upon rupture of the covering 

 membrane a dusty black-brown 

 spore-mass appears; spore-balls 

 ovoid to spherical, 17-25 n in 

 length; sterile cells tinted, ovoid 

 to spherical, small, rather com- 

 pletely covering the spores, 

 usually 4r-8 n in length; fertile 

 cells reddish-brown, ovoid to 

 spherical, usually 1, rarely 2 in 

 a ball, chiefly 12-16 ju in length. 

 On Allium. 



The first American description of the fungus was by Farlow ^ 

 in 1876. A second thorough paper was from Thaxter in 1889.** 



The myedium grows between the host cells. At maturity lateral 



Fig. 234. — Spores of U. cepulte genni- 

 nating. x, sporidia; 23, geriuinating 

 conidium. After Thaxter. 



