306 MASS. EXPERIMENT STATION BULLETIN 247 



Practical and theoretical information has been disseminated by letters 

 and directly by personal interviews. Tali<s and lectures are delivered 

 upon request of organizations and communities. The following types of 

 laboratory service are offered to residents of the state, at cost: 



1. Bacteriological analyses of food and food products, milk and milk 

 products, and water. 



2. Chemical analyses of milk and water. 



3. Preparation and distribution of viable and efficient cultures of 

 nitrogen-fixing bacteria for leguminous crops. 



4. Testing of nitrogen-fixing bacteria for quality. 



5. Bacteriological examinations concerning sewage disposal. 



G. Bacteriological examinations of swimming tank waters for purity. 



The Service is but in its infancy. However, during the time of opera- 

 tion some seven hundred examinations have been completed, and the vari- 

 ous types of analyses requested to date appear to justify the establishment 

 of the work. 



DEPARTMENT OF BOTANY 

 A. Vincent Osmun in Charge 



Tobacco Diseases. (W. L. Doran). 



Black Root-Rot. Study of soil reaction in relation to recovery after 

 infestation with Thielavia has been continued on the Tillson Farm plots and 

 in the greenhouse. In 1927, neither tobacco, alfalfa, nor timothy removed 

 enough lime from the soil to increase soil acidity. In 1928, limed plots 

 (lime last applied in 1923) on which timothy or alfalfa had been grown 

 two years were not as acid as similar plots on which tobacco had been 

 grown. Apparently the growing of alfalfa or timothy is not to be re- 

 garded as a cure for tobacco ''soil sickness" caused by too much lime 

 and resulting in black root-rot. 



The soil in limed plots treated with inoculated sulfur or sulfuric and 

 orthophosphoric acids had pH values of 5.6 to 5.8, while limed plots not 

 so treated had pH values of 5.9 to 6.0. The slight increase in soil acidity 

 was sufficient to reduce the infection of Thielavia. Only a trace of 

 black root-rot was found in 1927 on tobacco in limed plots to which acids 

 were applied in two consecutive years. Root-rot was severe on limed 

 plots not acidified. 



In 1928, the limed plots had pH values of 6.01 to 6.10, which is favor- 

 able to black root-rot; unlimed plots had 5.00 to 5.33, which is too acid for 

 black root-rot. It is evident that the soil made "tobacco sick" with black 

 root-rot because of too generous liming may require as long as six years 

 to return to an acid condition unfavorable to black root-rot. 



Temperature tank records in 1926 indicate that in soil with a pH value 

 of 5.9, black root-rot may be severe at soil temperatures below 75°F. 

 Above this temperature black root-rot is not of consequence. In 1927 

 and 1928, soil temperatures in a limed plot on the Tillson Farm were 

 generally low enough to favor infection of tobacco by Thielavia. 



Tobacco on limed soil acidified in two successive years by treatment 

 with sulfur or sulfuric acid and orthophosphoric acid was relatively 

 free from black root-rot. This was true also on limed soil treated with 

 acetic acid, but acetic acid does not permanently change the reaction of 

 the soil and hence the effect would seem to be due to disinfection by the 

 acid rather than to change in the pH value of the soil 



