210 MAINE AGRICULTURAL EXPERIMENT STATION. I9I4. 



another, one which was a typical specimen showing the decay or 

 necrosis at the stem end with more or less cracking of the sur- 

 face. The plants were dug up and examined about 4 months 

 after planting. The tubers produced in each case were small, 

 deformed and grouped in clusters close around the stem, largely 

 above the surface, with some of the aerial tubers or tuber Jike 

 outgrowths in the axils of the leaves and branches. The plant 

 obtained from the pitted tuber was the less severely attacked of 

 the two. In both cases the surfaces of the young tubers 

 showed the characteristic browning and necrosis at the stem 

 end, but no pitting or cracking was observed. 



Three tubers of a long, slender, purple-skin variety of pota- 

 toes, variety unknown, but locally known as "Blacks" were ob- 

 tained in Lewiston at the meeting of the Maine Seed Improve- 

 ment Society in December, 191 3. These were covered with 

 pits filled with Rhizoctonia threads and dead tissue. These 

 tubers were cut into 3 pieces and planted, making 9 pots in all. 

 When the plants were mature there was no evidence of pitting 

 on the crop produced, but many of the tubers were covered 

 with Rhizoctonia sclerotia. 



It will be seen, therefore, that what little experimental evi- 

 dence we have been able to secure by planting pitted tubers or 

 other tubers affected with Rhizoctonia, except in the case of 

 the tubers obtained from Nebraska and Wisconsin, fails to 

 support the assumption that Rhizoctonia is the cause of the 

 pitting. However, it must be remembered that the character of 

 the soil and the conditions under which the potatoes were grown 

 in the greenhouse in the experimental tests were quite different 

 from those where this form of the disease was observed in the 

 field. Moreover the appearance of the pitting only in the 

 presence of other injuries plainly due to Rhizoctonia would 

 seem to indicate that this fungus is in some way directly or indi- 

 rectly the cause of it. In the field, as has already been described, 

 the formation of a pit could be traced in various stages from 

 its beginning at a lenticel infected with a few threads of the 

 fungus. At the same time it is recognized that the presence of 

 considerable quantities of Rhizoctonia filaments constantly asso- 

 ciated with the pits is by no means conclusive evidence that it is 

 the primary cause of their formation. In this connection the 

 experiments described in the following section are of interest. 



