326 MAINS AGRICULTURAL, EXPERIMENT STATION. I907. 



portions had not become dry invariably showed myriads of 

 motile bacteria. As farther evidence that Rhisoctonia is prob- 

 ably not primarily the cause of the disease as it occurs in Maine 

 it should be noted that the occurrence and distribution of the 

 fungus is far out of proportion to the amount of "black-leg." 

 Rhisoctonia sclerotia are of almost universal occurrence on the 

 tubers everywhere in the State. Examination of the old potato 

 tops which had lain out all winter, in widely separated localities, 

 showed that the old, dried stems were invariably studded with 

 these same black sclerotia. Figure 50 is a fair representation 

 of the appearance of these stems from one field. However, 

 repeated searching during the summer over an 8-acre field 

 planted with seed from the same source failed to reveal but one 

 stem affected with "black-leg." 



Attempts to produce the disease in the field by inoculation 

 with pieces of diseased tissues and from cultures were without 

 success and greenhouse facilities with which to follow up the 

 matter with younger plants with control conditions were not 

 available. Therefore, little was accomplished other than de- 

 scribed above in determining the cause of the disease as it 

 occurs in Maine. 



The writer is fully aware that the foregoing adds little to 

 what is already known with regard to this class of potato stem 

 diseases, other than enlarging the range of distribution. How- 

 ever, this somewhat extended account is given with the hope 

 it will cause Maine growers to be on the lookout for potato 

 stem diseases and to report them at once to the Station with 

 samples for examination. In this way they will materially assist 

 in the studies which are now planned for the coming season. 



In conclusion it should be stated that so far as the present 

 knowledge of the disease as it occurs in this State goes there 

 need be no cause for serious alarm. The severe outbreaks 

 observed were largely on low, poorly drained soil, not well 

 adapted to potato culture. It is not believed that "black leg" 

 will ever become in Maine so serious a pest to handle as scab. 

 There is considerable reason to believe that it may be transferred 

 from one field to another with the seed, therefore seed from 

 infected fields should not be used. The suggestions with refer- 

 ence to the use of clean, smooth seed, disinfected with formalin 

 or formaldehyde, apply equally well here as in the case of scab. 



