364 Journal of Agricultural Research voi. xix.no.s 



fundamental principles of bacteriology and physico-chemistry : First, 

 the established fact that microorganisms in an active vegetative condi- 

 tion or just resuming activity are more susceptible to destructive agents 

 than when in a dry or dormant state; second, the law governing the 

 diffusion of dissolved substances whereby a solvent has a diluting effect 

 on any solute diffusing into it from a stronger solution. 



EXPERIMENTAL METHODS 



Numerous experiments with the use of dry heat (90° to 110° C. for 

 various periods) for the control of the blackchaff disease had indicated 

 that it was attended either with serious seed injury or else with incom- 

 plete control of the bacteria so as to render it unsatisfactory for field use. 

 Exposure to 105° C. for one hour killed all the bacteria, but it also killed 

 a very considerable part of the seeds, while in every case exposure to 

 temperatures between 90° and 100° C. failed to kill all the bacteria. 

 Earlier experiments with mercuric chlorid (1:1,000) and with copper 

 sulphate (1:1,000) begun by Dr. Smith were abandoned because many 

 seeds were killed by the mercuric chlorid and not quite all the bacteria 

 were killed by the copper sulphate. A number of experiments to de- 

 termine whether the formalin treatment for cereals might also be appli- 

 cable as a means of controlling the blackchaff disease showed marked 

 injury to the seeds but gave a fairly satisfactory control. The lesser 

 amount of seed injury growing out of long exposures as compared with 

 short exposures is what led to the discovery of the treatment described 

 in the present paper. 



Two parallel series of experiments were carried out — one, to determine 

 the effects on the blackchaff organism of various treatments, the other to 

 observe the effects of the same treatments on the germination of wheat. 

 Nine of the most widely grown wheat varieties were used in the latter 

 series: Turkey, Fultz, Marquis, Bluestem, China, Preston, Poole, Fife, 

 and Fulcaster, obtained through the courtesy of the Office of Cereal 

 Investigations. 



Treatments for the seed-germination tests were made as follows, 

 except as otherwise stated. Seeds counted out in sets of 100 were 

 placed in loose cheesecloth bags and soaked thoroughly for 10 minutes 

 in the solution to be tested. The surplus liquid was then drained off, 

 and the seeds were placed in covered moist chambers containing several 

 layers of filter paper previously rinsed with the same solution. After 

 definite periods of time the seeds were removed, spread out to dry over- 

 night, and planted the next day in flats or pots in the greenhouse. Un- 

 treated seeds were also planted as controls. Later in the course of the 

 work treated seeds were planted outdoors at the Arlington Experimental 

 Farm. 



