14 MASS. EXPERIMENT STATION BULLETIN 213. 



where no tobacco was planted last year. Four of them had wildfire this 

 year and four did not. The practice of sterilizing the beds should be 

 continued not only to destroy wildfire bacteria but also to kill other dis- 

 ease organisms and weed seeds. 



Sterilization of Sash and Plank. 



The writers (1: 76) in 1921 recommended that old sash and plank be 

 drenched with a Vr>o formaldehyde solution, and this was practiced by a 

 number of growers. Some painted the sash and used new plank. 



Data as to the benefits from this practice during 1922 are not very 

 conclusive because in most cases other sources of introduction were not 

 eliminated, but in a few cases under the writers' constant observation 

 clean plants were raised in 1922 under the same sash and with the same 

 sideboards (after sterilizing both) which had been used for badly dis- 

 eased beds in 1921. Danger of infection from contaminated sash is well 

 illustrated by the following experience of a Connecticut grower: His 

 seed-beds in 1921 were so heavily infected in June with wildfire that the 

 plants were destroyed. The sideboards were destroyed, the beds plowed 

 up, and the sash stored over winter in a tobacco barn. The grower in 

 1922 decided to take no chances of a wildfire infection and contracted 

 with a farmer who did not raise tobacco to grow sufficient plants for his 

 use. The farm on which the plants were grown was remote from any 

 tobacco fields or beds, new land was plowed and fitted, and old seed in 

 which there was no possibility of contamination was used. It might 

 be supposed that these precautions would insure freedom from the trouble ; 

 but as the farmer growing the plants had no sash, the sash used on the 

 beds in 1921 were taken from the first farm and used on the beds. They 

 were not sterilized, and shortly after the plants were up a very heavy in- 

 fection occurred on all the beds on which the sash were used. Wliile the 

 proof is not absolutely conclusive, the inference is justified that the sash 

 carried the bacteria. Unfortunately no beds without sash were grown 

 in this particular instance, but it might be said that the possibility of 

 contamination from other sources was slight indeed. 



The following laboratory experiment was made with the object of 

 determining how long the bacteria would remain alive on a piece of dry 

 wood such as a side plank or sash : — 



Experiment 8. — Small blocks of pine wood were sterilized and then soaked 

 for eight days in a pure culture of Bacterium tabacum in bouillon. Then they were 

 removed to dry, sterile tubes, where they quickly became dry and were kept so for 

 further tests. The experiment was begun July 1, 1921, and the blocks were kept 

 in the laboratory. At various intervals the blocks were tested for live bacteria by 

 dropping one in sterUe bouillon. They were still alive on September 10, but were 

 dead on December 3. Sometime between these dates the last of them died. Appar- 

 ently, then, they are able to live tliree months or more on dry wood. 



In this laboratory experiment, however, the conditions are not the 

 same as they would be in nature: (1) The wood is dried out more rapidly 



