226 AGRICULTURAL EXPERIMENT STATION. [Jan. 



view of their appearance on the same spots, and in the 

 relations described, it is pertinent to inquire if they may not 

 be forms of the same pleomorpliic fungus. Direct proof, 

 either for or against this hypothesis, is, however, still 

 wanting. 



No very definite directions for combating this trouble 

 can be given, in the absence of more complete knowledge 

 of the accompanying fungus forms than we yet have. As 

 both Septoria and. Oercospoi'a spores quickly germinate and 

 infect new hosts, that is, are summer spores, it is probable 

 that sprajdng the crop as soon as the spots begin to appear 

 may check its spread. It is probable that the " Eau Celeste " 

 would give good results. Leaves badly attacked should be 

 burned ; all refuse should be cleared from the field at the 

 end of the season, and burned ; and the same crop should 

 not be planted on the same ground or in its immediate 

 neighborhood, the following year. 



3. The rot of potatoes has been unusually serious on the 

 station plots, as throughout the State, during the season just 

 past. This disease, known as hlUjlil when it attacks the tops, 

 and as rot when the tubers are afi'ected, is due to a fungus of 

 the downy mildew group, Pliytopldhora iiifestans deBary. 

 Its abundance and destructiveness in 1889 have called out so 

 many descriptions and recommendations concerning the fun- 

 gus and means for checking it, that an extended account is 

 superfluous here. The fungus spreads very rapidly by 

 means of summer spores, but, so far as is known, does 

 not, like most of the downy mildews, produce resting 

 spores. Its only known mode of passing the winter is by 

 the hibernation of its mycelium in the host tubers. Special 

 care should be taken, then, to avoid planting "seed" pota- 

 toes which contain this hibernating mycelium, whose pres- 

 ence is commonly indicated by dark-brown sunken spots on 

 the surface of the tuber, beneath which the tissues are more 

 or less " rotted." A fuller account of this very fatal dis- 

 ease, by the present writer, may be found in Bulletin No. 6 

 of the Hatch Experiment Station of the Massachusetts Agri- 

 cultural College. 



The blight which appeared on the leaves of potatoes on 

 the plot devoted to scab experiments, as previously men- 



