340 MASS. EXPERIMENT STATION BULLETIN 260 



6. Bacteriological examinations concerning sewage disposal. 



6. Bacteriological examinations of swimming tank waters for purity. 



Studies on the Indio] Tolerance of the Colon-Aerogenes Group of Bac- 

 teria as a Possible Means of Differentiating Fecal and Non-Fecal Strains 

 Occurring in Drinking Water Supplies. (Ralph L. France). The results 

 to date are very promising and it is hoped that the study will supply a 

 more accurate method of testing water for fecal contamination. 



The laboratory is now in its second year of service and the indications 

 are that it is well established and conducted for the kind of work as- 

 signed to it. This type of supplementary investigational program will aid 

 materially in the value of the service. 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in Charge 



Tobacco Diseases. (W. L. Doran). 



Black Root-Rot. A paper on the effects of soil temperature and reaction 

 on growth of tobacco infected and uninfected with black root-rot has been 

 accepted for publication in the Journal of Agricultural Research for Decem- 

 ber I, 1929. 



In the field experiments, the pH values of soil in limed plots have 

 remained practically unchanged at about 6.0 for the past four years. 

 Neither alfalfa nor timothy, grown two seasons on limed plots, has 

 resulted in soil significantly more acid than has continuous tobacco. Of 

 the acidifying treatments of limed soil, the most effective were sulfuric 

 and orthophosphoric acids applied together in two successive years, and 

 sulfur (400 lbs. per acre) applied in two successive years. The applica- 

 tion of any of these treatments in only one year (1926) had but slight 

 effect, if any, on soil reaction after 1927. Examination of roots indicated 

 that black root-rot in these plots was suppressed in proportion to the 

 effectiveness of the acidifying applications. 



Yields on unlimed plots without acidification and with tobacco grown 

 continuously were 28 per cent greater than on limed plots (last limed in 

 1923). Yields on limed plots were increased by all the acidification treat- 

 ments as compared with yields on limed plots without acidification. Sul- 

 fur (200 lbs. per acre) applied in 1926 and 1927, and sulfuric and ortho- 

 phosphoric acids applied together in the same years gave the greatest 

 increases. 



Investigation of the use of various chemicals for the prevention of 

 black root-rot and other soil-borne diseases of tobacco seedlings has 

 continued. Acetic acid treatment of the soil was tested in several com- 

 mercial seed beds. In every case the treatment resulted in suppres- 

 sion of weeds and successful control of both damping-off and black 

 root-rot. It compared favorably with steam sterilization against which 

 it was checked. 



Tests with monochloracetic acid were not encouraging. Interesting 

 and promising results were obtained with pyroligneous acid. Experiments 

 were conducted with the object of adding to our knowledge of the effect of 



