92 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 



biius containing some 13,000 barrels of potatoes, grown in 5 r 

 6 different toiwns, were recently inspected by Mr. M. Shapova- 

 lov and the writer in Piscataquis County and no powdery scab 

 W'as found. However, potato growers in other parts of the 

 State should be constantly on the watch for the disease, es- 

 pecially if they have recently used seed from the districts now 

 known to be infested. In this connection it may be said that 

 there is probably less danger at present of obtaining powdery 

 scab from these sections than in the immediate past as the 

 system of inspection and certification established by the State 

 Department of Agriculture in cooperation with the Federal 

 Horticultural Board is designed to prevent the dissemination of 

 the disease from these infected districts to other parts of this 

 State or to other States, 



Cause oe the Disease. 



The organism, Spongospora subterranea (Wallr.) Johnson, 

 v/hich is responsible for the production of powdery scab is 

 quite different from the one which causes the ordinary type of 

 scab with which Maine potato growers have been acquainted 

 for many years. Powdery scab is produced by one of the 

 slime molds which latter belong to the lowest order of living 

 organisms, on the boundary line between the animal and vege- 

 table kingdoms. It is the same type of organism as that which 

 causes the well known club root of cabbage and allied plants. 

 The facts we know regarding its life history may be briefly 

 stated as follows : The earliest stage observed consists of a 

 simple protoplasmic body of the ameba type located within tiie 

 young potato cells. The nucleus of this ameba divides, and 

 generally in the early stages of the infection this is followed by 

 a division of the ameba itself, which process continues until a 

 number occur in one cell. According to Osborn* who recently 

 studied the matter quite carefully these amebse apparently da 

 not have the power to migrate from one cell of the potato to 

 another, but as the potato cell divides a part of those contained 

 in the original cell may go to each daughter cell resulting from 

 this division. Thus the new cells become infected as soon as 



* Osborn, T. G. B. Spongospora subterranea (Wallroth) Johnson. 

 Annals of Botany 25 : 327-341 Ap 191 1. 



