4 MASS. EXPERIMENT STATION BULLETIN 213. 



into the laboratory and transferred to other media they grew normally. 

 The result was about what one would expect when it is remembered that 

 few species of bacteria are killed by freezing. It is certain from data 

 presented below that freezing does not kill them while in the leaf in the 

 tobacco barn. 



On the Seed. 



It has been suspected by most workers who have investigated this 

 disease that the bacteria may survive the winter on or with the seed, and 

 that early infections in sterilized beds originate in this way. Although 

 this would seem possible, there is as yet no experimental evidence to prove 

 that such is the case in the Connecticut Valley. In Virginia, Fromme and 

 Wingard (3) find conclusive evidence that the organism of blackfire of 

 tobacco {Bacterium angulatum) overwinters in this way. Their evidence 

 for the wildfire organism, however, is not so convincing. A number of 

 experiments were undertaken by the writers for the purpose of determin- 

 ing the possibility of overwintering in this way. In the interest of brevity 

 these experiments need not be given in detail, but the results may be sum- 

 marized : — 



1. All attempts to isolate the organism directly from suspected seed 

 have failed. 



2. Suspected seed has been planted and no wildfire has appeared on the 

 seedlings where other sources of infection have been eUminated. 



3. Seed inoculated by soaking in a pure culture of the bacteria and kept 

 in a dry room aU winter produced only clean plants in the spring. 



4. In another experiment seed was artificially inoculated after it had 

 been sterilized and the bacteria killed by heat. The seed remained wet 

 from the culture for two weeks. In the spring it was sprinkled on healthy 

 leaves and wildfii-e resulted, but the conditions are not the same as where 

 seed is kept in a dry room. 



All the evidence in these experiments was negative and has only the 

 weight of such. The possibility is not precluded that there may be con- 

 ditions under which the bacteria may winter directly on the seed coat. 



There is no evidence that in nature a lesion may come in direct contact 

 with the seed. No one has ever reported seeing a lesion on the seed. It 

 is a well-known fact, however, that lesions do occur on the calyx of the 

 flower and on the seed pod. During 1921 in Connecticut and during the 

 late summer of 1922 in Massachusetts, pod lesions were found on plants 

 being kept for seed. Similar lesions were also produced by artificial in- 

 oculation. In threshing out the seed small broken bits of the pods remain 

 with the seed as chaff, and no amount of sifting and cleaning will remove 

 every particle of chaff. If the bacteria overwinter in the seed, it is probably 

 not directly on the seed but in these fragments of pods, etc., which are with 

 the seed. Since it is known that they survive the winter in leaf lesions, 

 there could hardly be any doubt that they could live over in similar lesions 

 on the pods. Fromme and Wingard (3:20) present experimental evi- 

 dence showing that the percentage of wildfire is increased by top-dressing 



