8 SEED STERILIZATION AND ITS EFFECT UPON INOCULATION. 



Table V. — Residual effect of disinfectants on bean, pea, rcicli, and harlcij seed. 



'J'reatment. 



Seed infected or sterile. 



Pea. 



r. 



,C(HI/,l . ._/ . 



sterile water 



Hydrogen peroxid. 



Sulphuric acid 



Mercuric chlorid. . . 



Flask seriet: 



Sterile water 



Hydrogen peroxid. 



Sulphuric acid 



Mercuric chlorid. . . 



+ + 



+ 

 + 



_6 



+ + 



+ 



+ 



Bean. 



+ 

 + 

 + 



+ + 



+ 

 + 

 + 



Vetch. Barley. 



+ + 



+ + 

 + 

 + 



+ 

 + 



+ + 



Colonies of Bacillus snbtilis de- 

 veloping after inoculation 

 into wash water. 



Pea. Bean. Vetch. Barley 



500 



250 



50 







700 



350 



300 



25 



1,000 



100 



50 



20 



1,000 



800 



700 



35 



600 



300 



100 



75 



800 



400 



250 







200 



200 



100 







600 



125 



50 







Seed killed. 



"* (Jermination delayed, seed injured. 



While there is no striking difference between the results obtained 

 by the two methods, there is an evidently greater jsenetration of the 

 disinfectant under the vacuum method of treatment. The bean; 

 treated Avith mercuric chlorid remained sterile with the application 

 of a vacuum and at the same time were two days later in germinating. 

 Throughout the two series there was less surviving contamination in 

 the vacuum series than in the flask series." 



There was further evidence that the disinfectant was less com- 

 pletely removed with the vacuum treatment. In the peroxid treat- 

 ments the average reduction of the number of Bacillus suhtilis col- 

 onies was G3 per cent in the vacuum treatment and 46 j^er cent in the 

 flask treatment ; in the sulphuric-acid treatments the average reduc- 

 tion was 87 per cent for the vacuum series and 58 per cent for the 

 flask series. Where mercuric chlorid was used the killing out of the 

 inoculated organisms was so nearl}^ complete that scarcely am' dif- 

 ference exists between the two series. 



The failure of barley to germinate after treatment with sulphuric 

 acid was surprising in view of the results obtained by Brown (see 

 p. C), but this suggests that the impermeable character of the barley- 

 seed coA'Cring may be abnormally developed in the case of the 

 particular variety used by Brown. The effect on BacAUus suhtilis 

 of the wash water from barley again showed that sulphuric acid is 

 more readily remoA'ed by rinsing than mercuric chlorid. 



The experiments show that the removal of air bubbles by a vacuum 

 does not entirel}^ solve the difficulty in seed sterilization and does 

 complicate the problem as regards the complete removal of the 

 disinfecting solution. This latter factor is of prime importance in 

 carrying on legume-inoculation experiments. The nodule organism 



"By selecting seeds after jiermination on agar it is comparatively easy to 

 secure sterile spronts for traiisplautiiig to other culture media. 

 [Cir. 67] 



