

[Vol. 9 



408 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



venetum, Macrosporium sarcinaejorme, Phomopsis Sojae, and 

 Actinomyces Scabies. These organisms were grown on potato 

 agar prepared according to the method of Duggar, Severy, and 

 Schmitz ('17), and spores were taken from cultures 10-15 days 

 old. 



The culture solution used in the hanging drops and in which 

 the sulphur particles were suspended was a slightly buffer 3d mix- 

 ture containing mannite, phosphoric acid, and sodium hydroxide. 

 The solution was prepared according to the method of Karrer 

 and Webb ('20), as follows: Stock solutions of M/5 mannite in 

 M/10 phosphoric acid and M/5 mannite in M/5 sodiam hy- 

 droxide were made. Equal quantities of the M/5 nannite- 

 M/10 phosphoric acid were placed in each of 10 flasks and suc- 

 cessively increasing proportions of M/5 mannite-M/5 sodium 

 hydroxide were added. The flasks were plugged with cotton, 

 sterilized at 15 lbs. pressure for 15 minutes, and allowed to stand 

 for a few hours. Titrations made by the colorimetric method 

 (Clark, '20) showed the mixtures to have the following range of 

 hydrogen-ion concentrations: P H 1.6, 2.4, 3.2, 4.2, 5.2, 5.8, 6.4, 6.8, 

 7.4, 8.4. 



EXPERIMENT I. TOXICITY OF THE FLOWERS OF SULPBUR 



Since sulphur in the form of flowers is insoluble in any solu- 

 tion that can be used for the growing of fungi, it was necessary 

 to test its toxicity in the form of suspensions. Twenty te:>t-tubes 

 were provided with pipettes that extended through the cork stop- 

 pers and to the bottoms of the tubes. By this means drops could 

 be transferred readily to the hanging-drop cells. These test- 

 tubes constituted a duplicate series of 10 each, and 5 cc. of each 

 of the slightly buffered solutions were added to the tubes so that 

 each tube represented a particular hydrogen-ion concer tration. 

 To one series .5 gm. of flowers of sulphur was added to eaoh tube. 



The technique of the planting of the hanging-drop cultures 

 was essentially the same as that used by Webb ('21) in his ger- 

 mination studies, and was as follows: Ground glass rings were 

 cemented to glass slides by means of parawax and petrolatum. 

 Two of these rings were placed on each slide, and 20 slides con- 

 stituted a series for each organism. This gave duplicate cultures 

 for each hydrogen-ion concentration. A few drops of the sul- 

 phur suspension to be tested for its toxicity were placed in the 

 bottom of the two cells. Another drop was placed on a clean 



