250 Journal of Agricultural Research Voi. xvu, no. 6 



So far no symptoms have been discovered by which mosaic can be 

 recognized in the dormant tubers ; nor has any effect upon the percentage 

 of germination or the time of blossoming been observed, although pre- 

 mature death may occur. 



The presence of mottling on the leaves is apparently modified by cli- 

 matic conditions. It was found by planting a part of the same affected 

 stock and strain in northern Maine and Colorado, that, whereas distinct 

 mottling occurred in northern Maine, none whatever could be detected 

 on the stock in Colorado during the same season. Similar tests were made 

 at Washington, D. C, and in northern Maine; and although some mottling 

 was noted at Washington there were a number of doubtful cases, while 

 the same stock in northern Maine showed very distinct mottling. Melhus 

 (7) found that progeny of plants which were mottled in northern Maine 

 did not show such s)anptoms in Iowa but showed symptoms of "curly 

 dwarf." 



For three successive seasons a number of lots of mosaic and healthy 

 seed potatoes have been divided and planted at the two experimental 

 farms of the Maine Agricultural Experiment Station. One of these 

 farms is located in the northeastern and the other in the southwestern 

 part of the state. Usually the part of a lot grown in southwestern Maine 

 showed considerably less mottling than the part grown in northeastern 

 Maine, while the reverse has never been noted. In two out of the three 

 seasons these differences have been very marked. On the other hand, 

 when the same lots which showed practically entire absence of mosaic 

 mottling in one location — in southwestern Maine — one season were re- 

 moved to the other and planted the following season, the mottling again 

 appeared in marked degree. 



TRANSMISSION STUDIES 



TRANSMISSION BY TUBERS 



Orton (9) cites a preliminary experiment and suggests the probability 

 of tuber transmission. Wortley {12) found that all tubers from affected 

 plants produced foliage with mottled leaves. Stewart {10) says that 

 mosaic is transmitted through the tubers. As pointed out before, Melhus 

 (7) showed that, under Iowa conditions, plants from diseased tubers 

 might not exhibit the mottling of the leaves but might show a dwarfing 

 and curling of the foliage similar to "curly dwarf." Murphy {8) says, 

 "Mosaic is perpetuated by planting the tubers from diseased hills." 

 These conclusions are confirmed by evidence which has been secured 

 by the writers and which will be presented later in connection with the 

 questions of hill selection and roguing. 



