SEED STERILIZATION AND ITS EFFECT UPON INOCULATION. 11 



poor agar (see page D), this medium giving the characteristic 

 growth of Pseudomonas radicicola. A third lot of untreated seed 

 was washed similarly to the treated seed and germinated under the 

 same conditions. 



The seed of six legumes (alfalfa, red clover, crimson clover, hairy 

 vetch, wax bean, and Canadian field pea) — one hundred seeds in each 

 of the three lots — was included in this test. Examination after four 

 days shoAved Pseudomo/ui.'^ radicicola present on the culture-treated 

 seed, both washed and unwjushed. Comparisons showed that washing 

 had been effective in removing about 75 per cent of the organisms 

 jilaced on the seed, but those remaining were capable of vigorous 

 growth. The untreated seeds, which were washed by the vacuum 

 process, were rendered no more free from contamination than those 

 rinsed by shaking in flasks or test tubes in the previous experiments. 

 The number of colonies was much less than in either of the treated- 

 seed series, but among these few (mostl}^ of the Bacillus subtUis 

 type) there again occurred occasional colonies closely resembling 

 the typical form of Pseudomonas radicicola. 



CONCLUSIONS. 



As a preliminary to legume-inoculation experiments, seed disin- 

 fection should bo practiced with special precaution. 



Some method of treatment to eliminate chance contamination with 

 the nodule organism is advisable in experiments where extremely 

 accurate checks are necessary. 



The usual methods of disinfection, employing metallic poisons such 

 as mercuric chlorid, are objectionable, it having been shoAvn that 

 these poisons cling to seeds even after they have been rinsed in 

 amounts sufficient to be harmful and often fatal to organisms placed 

 on the seeds for inoculation. 



Hydrogen peroxid has been found to be effective in eliminating 

 bacterial contamination, and its residual effect is much less harmful 

 than that of the other disinfectants tested. 



Approved : 



W. M. Hays, 



Acting Secretary of Agrictdture. 



Washington, D. C, July 22, 1910. 



[Cir. 07] 



o 



