134 AGRICULTUEAL EXPERIMENT STATION. [Jan. 



ground, to thirty-one per cent, on that unirrigated ; and fifty- 

 one per cent, of diseased ones on the manured ground, against 

 twenty-two per cent, where manure was not used. These 

 results indicate that an abundance of moisture favors the de- 

 velopment of scab, but can hardly be held to support the 

 view that it is the chief cawse of the disease. Beckwith con- 

 cludes from his experiments that an increased 3deld is nearly 

 always accompanied by an increase of scab ; and that any 

 marked change in the rapidity of the growth of the tubers 

 favors its development, a continuous growth from their first 

 formation to maturity being least favorable to the appear- 

 ance of the disease. The last point may, perhaps, be re- 

 garded as another aspect of Sorauer's view that a heavy 

 rain after drought especially aids the development of scab. 



Observations made at this Station during the past five years, 

 and detailed in its reports,* also bear interestingly on the 

 subject. The experiments were begun with a wholly diflfer- 

 ent end in view, but were vitiated the first year by the 

 appearance of scab, which has persistently appeared on the 

 same plats in every succeeding year. The first year, when 

 the land was freshly broken, the trouble was less severe, and 

 a diflference in severity was noticed on plats difierently fer- 

 tilized. Since the first year, the crop has been uniformly 

 scabby, but not more so in wet than in drier seasons. The 

 experiments thus far, while by no means conclusive in their 

 results, seem to point to peculiar soil conditions as the most 

 probable cause of the disease. 



In 1887 there appeared a paper by a Norwegian naturalist, 

 Brunchorst,f on a disease of potatoes common in that 

 country, and there called " Skurv," which he believes to be, 

 and which, from his description, seems to be, the same as 

 the German " Schorf " and the English and American " scab." 

 This writer states that the masses noticed by other investi- 

 gators in the dead cells of the tuber, and by them supposed 

 to be composed of disorganized cell-contents, are really the 

 resting condition of a parasitic organism, whose attacks 



* Second to Sixth Annual Reports of Massachusetts Agricultural Experiment 

 station, 1885-80. 



t Ueber eine sehr verbreitetc Krankheit dor Kaitoffelknollen. In Bergens 

 Mnseams Aarsberetning for 1886, p. 219. 



