214 AGRICULTURAL EXPERIMENT STATION. [Jan. 



2. The Potato Scab. 



In the report of this station for 1888, pages 131 to 138, 

 was given an account of the disease of potatoes known as 

 " scab," with a summary of the views held up to that time 

 as to its nature and cause. It was shown that, while the 

 characters of the disease are sufficiently marked and far 

 too familiar, its cause is still to be explained. On this 

 point three principal theories are held, which may be stated 

 briefly as follows: (1) the theory of W. G. Smith and 

 others, that the trouble is caused by the irritating action of 

 foreign substances in the soil ; (2) the view that it is due 

 to peculiar soil conditions; and (3) Brunchorst's claim that 

 it is caused by the attacks of a parasite belonging to the 

 slime moulds. Various American experiments were quoted, 

 bearing on the effects of the presence or absence of manure, 

 excess or deficiency of water, use of smooth or scabby 

 "seed," use of fungicides, and cultivation of light or dark 

 skinned potatoes. 



In the spring of 1889, arrangements were made for 

 experiments on the same plot on which the scab had ap- 

 peared for several years, — Field E, containing about three- 

 tenths of an acre. This plot, which had been ploughed the 

 previous fall, was ploughed again in the spring, and 

 divided into twenty-eight sections of three rows each, the 

 section being regarded as the unit, and each section being 

 treated, as nearly as possible, in a uniform manner. 



The w^hole plot, excepting section 1, at the south end, 

 was dressed with an application of ground bone and potash- 

 magnesia sulphate, at the rate of 600 pounds of the former 

 and 200 pounds of the latter per acre. In addition to 

 suggestions for the details of experiments drawn from cur- 

 rent theories and previous experiments, two were adopted 

 from other sources ; namely, to test the ofl'cct of tobacco 

 applied in the drill in the form of ground tobacco refuse, 

 and to observe the results, as to the development of scab, 

 of deep planting. Arrangements were made to facilitate 

 the irrigation of a part of the sections ; but, owing to the ' 

 extreme rainfall of the season, no use was made of the 

 means provided, and no comparison of the effects of excess 



