Cereals 297 



11,000 heads Plumb in 1886 determined the amount of smut 

 to be 8.4 per cent; in some fields he found as high as 20, 28, 

 and even 30 per cent. Kellerman and Swingle, counting 

 smutted heads in Kansas, found different fields to have 8, 

 15.3, and 18.3 per cent of smut, while single portions of a 

 field showed as high as 30 per cent. The loss in this country 

 in 1917 was estimated as approximately 91,000,000 bushels. 



The reasons for underestimation of oat smut are: 1, the 

 dwarfing of many of the affected plants, which thus re- 

 main unnoticed by a casual glance over the field; 2, the 

 fact that many smutted panicles remain invisible unless 

 unrolled from their enveloping leaves. 



It was proved as early as 1858 that infection can occur 

 only upon the very young oat plant; that older plants are 

 immune. It was later determined by Brefeld that the 

 plants are immune after the leaves have protruded 1 cm. 

 beyond the leaf sheath. From this and other experiments 

 it follows that practically all infection comes from smut 

 spores which are upon the seeds when they are planted. 

 These germinate, producing sporidia which infect the young 

 plant. The fungus develops in these plants throughout the 

 season without conspicuous effect until, at blossoming time, 

 the fungus seeks the ovaries and the glumes and appears 

 again as the familiar black spore masses. 



Any treatment which kills the spores upon the seed with- 

 out materially injuring the seed itself results in a clean crop. 



The copper sulfate treatment endangers germination of 

 oats. The hot water treatment is less convenient than the 

 formalin treatments which are thoroughly satisfactory. 

 See p. 270. 



Covered-smut {Ustilago levis (K. & S.) Magn.), — This 

 differs from the loose smut in the less complete destruction of 

 the flowers and in its less dusty spore masses, which are also 

 blacker than in the loose smut. The smut masses are usually 

 limited to the parts within the flowering glume and the palet 

 or to the bases of these. 



The treatment is that given for loose smut. 



