36 



BOTANY AND PHARMACOGNOSY. 



They do not germinate at once, but on keeping them for six 

 months to a year they germinate readily on a culture medium 

 of potato, and retain their power of germination for years. 



Rust Fungi. The Rust Fungi are parasitic on higher 

 plants and produce a thread-like, branching, cellular mycelium, 

 which develops in the tissues of the host. They differ especially 





Fig. 23. Spores of various Smuts, i , L'5(7ago fong-fsswna growing on the reed meadow- 

 grass {Panicularia americana) ; 2, Ustilago Maydis ivom Indian com (Zea Mays); 3, Usiilago 

 Oxalidis on the yellow wood-sorrel (Oxalis siricta); 4, L'stilago utriculosa on the Pennsyl- 

 vania persicaria (Polygonum pennsylvanicurn) . 



Fig. 24. Germination of spores, s, J/sZi/agOM^ncwtea, in water, showing promycelium 

 and sporidia; 6, Doassansia opaca from the broad-leaved arrow-head (Sagittaria laiifolia) 

 in water, showing promycelium, sporidia, and secondary sporidia which are falling off; 7, 

 Ustilago avencB from oat (AverM saliva) in horse dung, showing promycelium, and lateral 

 "infection threads" or hypha;; 8, germination of a sporidium of Usiilago Sorghi into an in- 

 fection thread; 9, small portion of a group of sporidia developed from promycelium of Toly- 

 posporium eriocauli in potato agar; 10, cross-section of epicotyl of broom-corn infected by 

 Ustilago Sorghi showing mycelium ramifying through parenchyma cells of the cortex. 

 After Clinton. 



from the other Fungi in producing resting spores known as 

 TELEUTOSPORES. These spores consist of one or more cells sur- 

 rounded by a thick black wall, and they produce the " black rust " 

 seen on foliage at the end of the season. 



