GENERAL MORPHOLOGY OF PLANTS 



formed on the pro mycelium germinate and the germ tube enters the 

 oat seedling at the base of the first leaf sheath. In the case of the 

 loose smut of wheat and barley the method of infection is different. 

 At the time the wheat or barley is in flower, the smut on the affected 

 plants in the field is just ripening, and spores are blown from the 

 smutted heads to the open flowers of healthy plants. The spores 

 lodge on the feathery style of the flower and germinate. They do 



( 



Fig. 241. 



Loose smut of barley (Ustilago 

 nuda). % diameter. 



Fig. 242. 



Bunt or stinking smut of wheat 

 (Tilletia tritici). Note the flaring 

 position of the palse. 



not produce a promycelium, but the germ tube of the spore enters 

 directly into the style, and passes down into the ovary, where it 

 forms a small amount of dormant mycelium which, however, does 

 not injure the grain, so that it ripens with the dormant mycelium 

 of the smut imprisoned. When these grains of wheat are sown, 

 the dormant mycelium begins to grow as the seed germinates, 

 and passes through the scutellum into the shoot. It then con- 

 tinues to grow along with its host, as in the case of the oat smut. 

 Beside the loose smut of barley there is another, the covered smut, 



