12 BULLETIX 1029, V. S. DEPAKTMEXT OF AGRICULTURE. 



A limiting factor in the use of mercuric-chloricl solution is the fact 

 that complete contact with the seed coats is usually prevented by the 

 presence of small air bubbles. To overcome this difficulty Hutchinson 

 and Miller (4) conducted their seed treatments in partial vacuimi, 

 but with only limited success. Since two trials with infected seed by 

 this treatment in 1 : 500 mercuric chlorid gave no better results than 

 parallel experiments at atmospheric jDressure. the method was aban- 

 doned (see Table IV). 



In order to overcome this difficulty in another way the seed was 

 soaked in water previous to treatment (method 3). The action of 

 the fungicide on the seeds was more rapid than with the unsoaked 

 seed, marked injur}'' resulting from treatments of more than 30 min- 

 utes' duration. At this point, however, the disinfection of diseased 

 seed was no more complete than with similar exposures of unsoaked 

 seed. 



In the fourth method of treatment, where seeds were rinsed in 

 alcohol before exposure to the mercuric-chlorid solution, the action of 

 the disinfectant was hastened somewhat, injury to the seed being 

 pronounced after a treatment of one hour (see lot No. 4-19, Table 

 IV). The method appears to be no more effective than the first, how- 

 ever, in eradicating the fungus from infected seeds. 



The results with mercuric chlorid may be siunmarized as follows : 

 With most lots of seed used a soaking of one hour in a 1 : 500 solution 

 followed by rinsing in water caused very slight seed injury. One 

 lot, however, was injured considerably by this treatment. Treatment 

 was necessary for two hours for complete eradication of the fungus 

 in the case of one lot of infected seed, and in another lot treatment 

 for three hours was insufficient to attain this result. Other methods 

 used with mercuric-chlorid solution — (1) soaking in the disinfectant 

 without rinsing after treatment, (2) presoaking in water before treat- 

 ment, (3) dipping in alcohol before treatment, and (1) treatment in 

 partial vacuum — did not appear to be superior to the first. For 

 general use soaking for 30 minutes in a 1 : 1,000 solution, followed by 

 rinsing in water, is advisable. Most lots of seed will stand a 1 : 500 

 solution for a somewhat longer time, but preliminary trials should 

 be made before this stronger treatment is applied. 



SUMMARY OF LABORATORY SEED-TREATMENT EXPERIMENTS. 



The data presented justify the conclusion that no known method 

 of cabbage-seed disinfection can be relied upon for the complete 

 eradication of the black-leg fungus, Phoma ling am ^ without severe 

 injury to the seed. It is also evident that different lots of seed vary 

 widely in their relative susceptibility to injury from seed treatment. 

 This forces one to be the more conservative in recommendations for 

 general practice. The results of experiments lead the writer to 



