ANNUAL REPORT, 1930 241 



water supplies. It miglit be of value, if the laboratory appropriation could 

 be increased sufficiently to finance the undertaking, to make sanitary in- 

 spection of the water supply and environment in some of these districts 

 having unsafe water. 



The legume culture collection has been kept intact and propagated as 

 in past years, for the purpose of distributing to farmers needing this 

 material for legume inoculation. Nearly all cultures furnished were for 

 inoculating alfalfa. 



The miscellaneous examinations made during the year include examina- 

 tions of milk for garget, streptococci and other organisms causing inflam- 

 mation of the udder, chemical analyses of milk, and examination of food 

 products for organisms causing unnatural spoilage. 



The Indol Tolerance of the Colon-Aerogenes Group of Bacteria as a 

 Possible Means of Differentiating Fecal and Non-Fecal Strains Occurring 

 in Drinking Water Supplies. (Ralph L. France). The work to date in- 

 dicates that in order to establish a more uniform set of results for the 

 determination of the possible use of the indol tolerance as a test, it is 

 necessary to make some clianges in methods and a more complete study of 

 the biochemical activities of the various strains. "With these studies fol- 

 lowed through, it is anticipated that the difficulties already expressed may 

 be eliminated, making it possible to obtain inore consistent residts. 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in charge 



Tobacco Black Root-Rot. (\V. L. Doran). Soil in plots last limed in 

 1923 still had pH values favorable to infection by Thielavia in 1930. 

 Neither alfalfa nor timothy was more effective than tobacco in lowering 

 the pH value of over-limed soil. Soil acidity of limed plots was increased 

 somewhat even four years after the application of sulfur. As in pre- 

 vious years, there was less black root-rot in limed plots to which sulfur 

 or acids were applied in 1926 and 1927 than in limed plots not acidified. 



There was not much, if any, less black root-rot of tobacco following 

 the hay crops than in plots of continuous tobacco. 



Yields of tobacco in plots limed were 27 per cent less than yields in 

 plots not limed. Loss caused by lime applied in 1923, has been decreasing 

 .since 1925. Increased yields in limed plots resulting from the application 

 of acids or sulfur were less in 1930 than in earlier years. 



The application of sulfur to a field in which the soil had an initial pH 

 value of 7.1 lowered the pH value to 6.5, but this was not enough to affect 

 black root-rot or growth of tobacco. 



An application of orthopho.sphoric acid lowered a soil pH value from 5.9 

 to 5.0, but black root-rot was nevertheless severe. It is apparent that other 

 factors than or in addition to the hydrogen ion concentration of the soil 

 are concerned. 



Tobacco Brown Root-Rot. (W. L. Doran). In the second or third year 

 of tobacco following alfalfa, timothy or alsike clover, there was little and 

 in most cases no brown root-rot. The brown root-rot effect of these hav 



