THE BASIDIUJ\r FUNGI (r.ASIDIO.An'OETES) 241 



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

 ticularly clestructi\-e to the grains and arc widely distributed. 

 In the United States it is estimated that the injur\' caused by 

 smuts to wheat, oats, and barley exceeds |2.5,00(»,(MI0 annually. 

 The oat smut i^rxtilni/d Aoence') 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 indieation that the 

 smut mycelium has previously permeated 

 the host. The snuit 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 germmation of 

 these heavy-walled spores a short hypha 

 is produced. This soon pro(hu-es four 

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

 thin-walled spores appear at about the 

 same time that oat seedlmgs are growing, 

 they produce hyphse ^^llich penetrate the 

 host plant. Under favorable growing con- 

 ditions the smut mycelium, which conthi- 

 lu^s 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 hea^■y resistant 

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

 lie upon the ground in the fields until fa\-oral)le conditions for 

 growth occur. Probably tlie 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 ( 1?)2° to loo°F.), or with water 

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



1 " The Grain Smuts.-- Fanners' Bulletin 75, U. S. Dept. Agr., lSii8 ; "The 

 Smuts of Grain Plants,'- Bulletin 122, Jlinn. Alt. Exp. Sta., 1911. 



Fig. I'.iii. A stage in 



tlie loose smut of oats 



{Ustiliigo ^i-vence) 



The small hypha that 

 is produced liy the ger- 

 minating spore soon 

 produces bud-like co- 

 nidia. l/lreatly magni- 

 fied. After Du2:2:ar 



