346 Journal of Agricultural Research voi. vi, no. 10 



conditions favorable to sporulation often become so badly infected that 

 they become a dull-black, the tubers having the appearance of having 

 been dusted with soot. Several such bins were observed in Maine in 

 May and June, 1914. 



In case of slight infection in the field the infected areas are often 

 found in isolated spots close to the stem end of the tuber. This was the 

 case in practically every infected tuber harvested from the silver-scurf 

 experimental plot at Caribou, Me., in the fall of 1914 and coincides with 

 the observations of Appel and Laubert (i). While no reasons for this 

 phenomenon are given by these investigators, from experiments and 

 obser\^ations so far made it appears that infection is brought about 

 through contact of the stem end of the young tuber with the infected 

 mother tuber (PI. XLVIII). This is indicated by the fact that in many 

 cases where there was but slight contact only small areas about the 

 point of the stolon attachment showed infection, while in the case of 

 extensive contact infection was more widespread. It is further indi- 

 cated by the fact that only one or two tubers closest to the mother tuber 

 showed infection in counts made when the crop was about three-fourths 

 grown, while in counts made later, after the conidia had become gener- 

 ally distributed, a large percentage of the tubers were infected. 



Although infection appears to take place through the stem end, both 

 stem ends and eye ends are subject to infection, general infection of 

 both resulting from artificial inoculations. 



In view of the fact that investigators like Bohutinsky (3) have attrib- 

 uted to 5. airovircns foliage symptoms such as leaf roll, mosaic, etc., 

 inoculations upon stems, stolons, and roots of the potato plant were 

 made, both under field and greenhouse conditions. Two distinct pro- 

 cedures were followed: In one set of experiments viable spores were 

 sprayed upon the stems, stolons, and roots; in the other virile mycelium 

 was inserted into the inoculated portions. Checks were also run. 

 Experiments in this order were run during 1914 and 191 5, and in every 

 case the inoculated plants behaved like the checks — viz, no perceptible 

 infection occurred — showing again the inability of this organism to 

 invade the vine tissues of the host. 



METHODS OF DISSEMINATION 



The fungus lives over by means of the mycelium, conidia, and sclerotia 

 within the infected areas, so that under favorable conditions of moisture 

 and temperature sporulation occurs and infection may spread even in 

 storage. Not only do the infected tubers carry the disease to new sec- 

 tions, but they may carry it over from one season to another in the soil 

 and in this way infect the new crop. This was the case in the author's 

 field studies in Maine, viable conidia being found on the surface of 



