CEREAL PESTS PARASITIC FUNGI 515 



Infection of the host takes place during the seedling stage, some 

 time before the seedling emerges above the ground, from spores 

 attached to the seed or in the soil closely surrounding the seedling. 

 The presence of the fungus is not manifest until the wheat spike 

 emerges from the sheath, and even then may be overlooked by the 

 ordinary observer. When the spikes are maturing, the glumes of 

 those infected stand somewhat apart from the smutted ovaries. 

 On removing the glumes the infected ovaries are found to be grayish 

 black in color, swollen and more spherical in form than the normal 

 kernel. These bodies crush easily between the fingers to a powder, 

 which is a mass of fetid spores, the chlamydospores, and are the 

 last stage in the life-history of the fungus (Fig. 158). The limit of 

 viability of these spores is not known, but Humphrey has germinated 

 them after a resting period of 12 years. 



On germination a germ tube is formed which develops a promy- 

 celium. From this is produced the second stage of the fungus in 

 the form of sickle-shaped primary sporidia, usually 8 in number 

 from each promycelium. These fuse in pairs, back to back, forming 

 H-shaped bodies which may become detached. They germinate and 

 give rise to secondary sporidia which are able to infect a germinating 

 wheat kernel when in contact with it. If no susceptible host kernel 

 is present, a crop of tertiary sporidia will be produced. 



Bunt of wheat has received more study than any other 

 cereal smut, and has been the cause of greater financial 

 loss. In occasional epidemics the infection runs as high 

 as 40 to 70 per cent of the crop. Such losses are, however, 

 in most places unnecessary, as the seed treatments for this 

 smut are usually very effective. The annual loss from 

 bunt of wheat in the United States is reckoned at ten to 

 twenty million dollars. In 1902, in the state of Wash- 

 ington alone, it is estimated that wheat bunt caused a 

 loss of two and one half million dollars. 



560. Loose smut of oats (Ustilago avence, Jens.). - 

 This smut occurs wherever oats is grown, and in this 

 country was probably once the most serious pest of the 

 oat crop. Now much loss is avoided by seed treatment. 



