102 
Journal of Agricultural Research 
Vol. XXV, No. a 
In addition to mosaic symptoms being masked or modified by regional 
differences in weather ana climate, there are differences between regions 
in regard to the amount of degeneration diseases and the rate of their 
spread in commercial fields. This is shown by local observations and by 
comparing representative lots from different regions when grown in the 
same place. Differences are apparent in three groups of lots from three 
counties of New York (j, p. n). The writers have reported a difference 
between different parts of Maine with mosaic spreading less in the St. 
John River Valley where aphids were less numerous (41, p. 75). This 
difference disappeared in 1921 with a heavy infestation of aphids in that 
valley, as is described in connection with certain data on isolation (Table 
XXVIII, field 38). Similar regional differences have been described by 
Murphy (29, p. 35-36 , 59-67) and Quanjer (, 39 , p. 143). 
The second-generation plants to the lots grown in Maine and Long 
Island, as noted in a foregoing paragraph (p. 101), were grown again in 
Maine, where the chief difference between these lots consisted in a higher 
percentage of leaf roll in the Long Island stock than in the duplicate 
Maine lots, which had no leaf roll. 
In 1921 a Green Mountain lot grown in Maine in 1920 was divided 
into five parts, which were planted, respectively, between mosaic Bliss 
Triumph rows in northeastern Maine and in southern Maine, between 
Irish Cobbler leaf-roll rows in these two places, and on Long Island 
between Green Mountain rows both all-mosaic and 25 per cent leaf roll 
(Table XXVI). In 1922 the Long Island part when grown in north¬ 
eastern Maine was 60 per cent mosaic and 75 per cent leaf roll, while 
at the same place the other stocks showed less disease (Table XXVI). 
Similar exposure to leaf roll and mosaic at the two Maine stations was 
made in 1921 with a Bliss Triumph lot and an Irish Cobbler lot, and a 
comparison in 1922 in northeastern Maine showed that a slightly greater 
spread of mosaic had occurred in northeastern Maine and a markedly 
greater spread of leaf roll in southern Maine (Table XXVI). 
Table XXVI .—Spread of mild mosaic and leaf roll in three places 
Variety. 
Location in 1921. 
Disease in 1922. 
Mosaic. 
Leaf roll. 
On Long Island between Green Mountain 
Per cent. 
62 
Per cent. 
75 
Green Mountain 
rows 100 per cent mosaic and 25 per cent 
leaf roll. 
In southern Maine between mosaic rows. . . 
31 
0 
In northern Maine between mosaic rows. . . 
57 
0 
In southern Maine between leaf-roll rows... 
40 
5 ° 
In northern Maine between leaf-roll rows... 
40 
3 
In southern Maine between mosaic rows. . . 
44 
0 
Bliss Triumph 
In northern Maine between mosaic rows. . . 
56 
0 
In southern Maine between leaf-roll rows... 
26 
1 9 
In northern Maine between leaf-roll rows... 
55 
8 
In southern Maine between mosaic rows. . . 
0 
0 
Irish Cobbler. 
In northern Maine between mosaic rows. . . 
2 
0 
In southern Maine between leaf-roll rows... 
2 
14 
fn northern Maine between leaf-roll rows... 
23 
4 
