218 PLANT DISEASES 



STINKING SMUT OF WHEAT 



(Tilktia tritid, Winter. 

 Tilletia caries^ Tulasne.) 



A destructive fungus to the wheat crop, inoculating the 

 young plantlet, and growing along with it without produc- 

 ing any external evidence of its existence, except perhaps 

 just a deeper tinge of green in the leaves, until the wheat 

 is in bloom, when the rigid, erect ear and spreading florets 

 and scales betray the presence of the parasite. The spores 

 are produced in the ovary or grain, and, as a rule, every 

 grain in the ear is diseased. When mature the mass of 

 spores liberated on crushing a diseased grain between the 

 fingers is black, with a tinge of olive, and possesses a very 

 strong, disagreeable smell, somewhat resembling rotten 

 fish, especially when moistened. 



The spores are always produced at the tips of branchlets 

 of mycelium, which do not become gelatinised. The epi- 

 spore, or outer wall of the spore, is furnished with thin 

 raised ribs, which are so arranged as to form a network 

 on the surface of the spore. Germination takes place 

 readily when the spores are placed on a damp surface, an 

 elongated promycelium being produced in the air, which 

 bears a tuft of 7 to 12 narrow, elongated, secondary spores 

 at its apex. These secondary spores usually become con- 

 nected in pairs by the outgrowth of a narrow neck from 

 one to the other, and when completed resemble the letter 

 H. The secondary spores that fuse in pairs germinate at 

 once, some producing a very slender thread or branch of 

 mycelium ; others give origin to curved sporidia, which in 

 turn emit a delicate germ-tube. Both these conditions 



