422 



[Vol. 9 



ANNALS OF THE MISSOURI BOTANICAL GARDEN 



the bottom of the ring. The filter-paper was saturated with 

 water. Spores of Sclerotinia cinerea were placed in a drop of the 

 culture medium without sulphur, on a cover slip which was in- 

 verted over the cell. The cells were not sealed at the top or 

 bottom. 



In the same Petri dish sealed cells were prepared. This was 

 done for each hydrogen-ion concentration. The Petri dishes 

 containing the cultures were arranged in a moist chamber through 

 which air was passed. This experiment was conducted at room 

 temperature and the percentage of germination noted titer 18 

 hours. The results are given in table in. 







TABLE III 









PERCENTAGE OF GERMINATION* 







SCLEROTINIA CINEREA 





Ph 



Ground flowers of sulphur 



Hydrophobic c 



olloidal sulphur 





-0 2 



+ o 2 



-Oj 



H-Os 



2.4 



40 



38 



34 



24 



3.2 



64 



49 



17 



10 



4.2 



68 



31 



8 







5.4 



65 



24 



11 







5.8 



62 



46 



54 



32 



6.4 



58 



49 



48 



44 



•Average of triplicate cultures. 



Another experiment was conducted, in which a weak suspension 

 of hydrophobic colloidal sulphur which did not inhibit ilie ger- 

 mination of spores of C olletotrichum Gossypii at any hydrogen- 

 ion concentration was aerated for 24 hours. Air from which the 

 oxygen was removed with pyrogallol ■ was passed through a du- 

 plicate series. The toxicity was determined with spores of C. Gos- 

 sypii in closed-ring cells in the same manner as in Experjnent I. 

 Likewise, a similar series was arranged, using an aerated sus- 

 pension of flowers of sulphur. The cultures were incubated at 

 22° C. and the percentage of spore germination determined after 

 18 hours. The results are recorded in table iv. 



The results of these tests prove conclusively that the toxic 

 property of sulphur is due to an oxidation product and that finely 

 divided sulphur is more readily oxidized at ordinary temper- 

 atures than the ordinary sublimed sulphur. 



'One part pyrogallol, 5 parts NaOH, and 30 parts H 2 0. 



