88 



in the course of time by officers of the Experiment Stations who are 

 investigating the disease. Tbe following notes on the subject are taken 

 from tbe Bulletin of ihe Kingston, Rhode Island Agricultural Experi- 

 ment Station, Nos. 26,33 and 40. W. H. 



The valuable and carefully conducted investigations by Bolley ^ and 

 Thaxter - seem to have conclusively established the tact that the dis- 

 ease of the Irish potato, known as the potato " scab" is the direct result 

 of the development upon the tuber of one or more fungi or minute 

 plant organisms. Heretofore this disease had been attributed by various 

 investigators to a number of different causes and the many theories and 

 practical observations on record, furnish by their contradictory nature, 

 conclusive evidence that the character and cause of the disease was not 

 understood. Now that the direct cause has, in all probability, been 

 ascertained, many of the heretofore conflicting observations have found 

 their explanation or have been discarded by some as probably unreli- 

 able, because no satisfactory explanation for them has yet been offered. 



It is not our purpose to discuss at length all of these theories and 

 observations, extended references to which may be found in the papers 

 by Humphrey^ , Thaxter^ and Bolley^ . Four of these discarded theo- 

 ries as to the direct cause of the potato scab are the following: " (1) 

 mechanical irritation; (2) damages resulting from insect agencies; (3) 

 chemical erosion or irritation; (4) excess of moisture." It is a matter 

 of common observation that if the surface of a plant or tree is injured, 

 nature at once attempts to cover or repair the injured place by produc- 

 ing an abnormal growth about the point of the injury. In fact the four 

 above mentioned theories were based upon the idea that refuse materials, 

 coarse manures, chemical manures, and among them those which tended 

 to set free ammonia within the soil, as well as an excess of moisture and 

 and insect depredations, were all capable directly or indirectly, of 

 imparting injury to the surface of the growing tuber and thus engen- 

 dered the disease. It is self-evident that these theories in light 

 of the lecent investigations of Bolley and Thaxter are no longer 

 tenable, or rather that they do not explain the direct cause of the scab 

 disease. 



From what has been learned by various investigators up to date, 

 in relation to the potato scab, it appears: (1) That the scab is caused 

 directly by the growth of a fungus upon the potato tuber. (2) That 

 if the " seed" tubers and the soil are from the germs the crop will 

 remain free from the scab if not contaminated by germs introduced in 

 some manner as upon manures, implements of tillage, etc. (3) That 

 the disease is liable to be spread by barn-yard manure. (4) That 



1. See Agricultural Science, Vol. IV, No. 9, p. 243. Vol. IV, No. 10, 

 p. 277, and Buls. 4 and 9 of the N. Dak. Agr'l. Exp't Station. 



2. An Kpts. Conn. Agr'l Exp't. Station for 1890, p. 81 and 1891, p. 153 

 and Bulletin 105. 



3. Oospora scabies is the name applied by Thaxter to the fungus of 

 " deep" scab. 



4. Sixth An. Rpt. Mass. State Arg'l Exp't Station, 1888, pp. 131-138. 



5. 1. c. 



6. 1. c. 



