conspectus: methods of control 69 



of the stone fruits, e.g., apricots and plums, and various wild 

 plants of the Family Rosacece, must be inspected because these 

 also are subject to the blight. 



The introduction of diseases transmitted by way of seeds, 

 bulbs, and tubers may be avoided by obtaining these from 

 plants not subject to the disease. As this freedom cannot 

 always be known, bulbs and tubers should be inspected criti- 

 cally before planting, and firm-coated seeds should be soaked 

 for 15 minutes in 1:1000 mercuric chlorid water; thin coated 

 seeds susceptible to mercuric chlorid, e.g., wheat, in 1 : 1000 

 copper sulphate solution (20 minutes) followed for a moment 

 by milk of lime; or exposed to formaldehyd (40 per cent, for- 

 malin 1 part, water 400 parts, for 10 minutes and then held moist 

 for some hours). In case of five plants (cabbage, maize, wheat, 

 barley and oats) we know positively that the diseases are trans- 

 mitted on the seed and this is probably true for several others — 

 peas, beans, soy beans, cucumber (angular leaf spot^, sorghum, 

 orchard grass. All shrivelled seeds should be screened out before 

 planting. Dry beans will endure at least 10 minutes exposure 

 to 1:1000 m.ercuric chlorid water and germinate freely. I have 

 not tried longer exposures. The germination of wheat is in- 

 jured even by 10 minutes exposure to 1:1000 mercuric chlorid 

 water and very seriously by ^200 formalin water, and also 

 by heavy doses of copper sulphate such as have been recom- 

 mended for the elimination of smuts. A. G. Johnson has re- 

 cently recommended hot dry air for the destruction of fungous 

 and bacterial parasites on various grains, but tried on wheat 

 for black chaff I found that either it seriously injured germina- 

 tion or failed to destroy all of the bacteria. It may serve ad- 

 mirably, however, for plot experim.ents where the aim is simply 

 to procure sound grain for subsequent field sowings, since here 

 a loss even of one-third of the seed grain is of no consequence 

 in comparison with the end in view. Formaldehyd (formalin), 

 if properly used, destroys all of the black chaff organisms 

 on the surface of wheat kernels (Fig. 50) but kills som.e of the 



^ ■ I saw remarkably virulent development of Bacterium lachrymaus this 

 summer [in Wisconsin] introduced on seed and spreading rapidly" (L. R. Jones, 

 1919: Letter to the author). 



