THE BASIDIUM FUNGI (BASIDIOMYCETES) 241 



231. The smuts. All the smuts are parasitic. They are par- 

 ticularly destructive to the grains and are widely distributed. 

 In the United States it is estimated that the injury caused by 

 smuts to wheat, oats, and barley exceeds $25,000,000 annually. 

 The oat smut (TJstilago Avence) is present in almost every 

 field of oats. It is generally recognized by means of the black 

 sticky masses of spores that form in the 

 positions previously occupied by the devel- 

 oping grains (Fig. 195). The spore mass, 

 however, is the external indication that the 

 smut mycelium has previously permeated 

 the host. The smut usually matures at 

 about the time the oat heads are in full 

 flower, and prevents the normal develop- 

 ment to such an extent that the annual 

 damage in this country is estimated to 

 reach $6,500,000. Upon germination of 

 these heavy-walled spores a short hypha 

 is produced. This soon produces four 

 thin-walled spores (Fig. 196). Since these 

 thin-walled spores appear at about the 

 same time that oat seedlings are growing, 

 they produce hyphae which penetrate the 

 host plant. Under favorable growing con- 

 ditions the smut mycelium, which contin- 

 ues its growth throughout the host, does 

 not markedly retard the growth of the infected oat plants. 



The spores that are formed in the heads have heavy resistant 

 walls. They may adhere to the grains, lie in the granaries, or 

 lie upon the ground in the fields until favorable conditions for 

 growth occur. Probably the grain used for seed is itself one of 

 the chief means of spore distribution. It has been found that by 

 treating seed oats with hot water (132 to 133F.), or with water 

 containing four tenths per cent formalin, the smut may be killed. 1 



1 " The Grain Smuts," Farmers' Bulletin 75, U. S. Dept. Agr., 1898; "The 

 Smuts of Grain Plants," Bulletin 122, Minn. Agr. Exp. Sta., 1911. 



FIG. 196. A stage In 



the loose smut of oats 



(Ustilago Avence) 



The small hypha that 

 is produced by the ger- 

 minating spore soon 

 produces bud-like co- 

 nidia. Greatly magni- 

 fied. After Duggar 



