348 LINDSTROM, GENETICAL RESEARCH WITH MAIZE ' 
Tests by Emerson accumulating since 1912 and reported in 1921 show 
that Pl pl and Yy are linked giving 24.2 to 30 per cent crossing over. 
Additional data by Anderson (1921) show a crossing-over percentage 
of 29.7 for these factors. 
Anderson also reports 10.0 per cent crossing over for the Pl-Sm fac- 
tors and 36.8 per cent for the Y-Sm factors. By means of threepoint 
tests the following order and distances of the factors in this group have 
been established: — 
BETEN EUER SPI 10.0 Sm 
y 36.8 sm 
Some very recent work by STROMAN (1923) has added the Ww factor 
(W,w,) pair to this group. He finds that Yy and Ww show approxima- 
tely 42 per cent crossing over. This may be the same linkage as that re- 
ported by KEMPTON (1917) the factors of which were not then indenti- 
fied. A very limited amount of data on the PJ pl and Ww relationship 
shows about 25 per cent crossing over. This work would indicate the 
following relative position of the Ww pair of factors on this chromo- 
Va 
some, . — 
. 
Pl 25 WI 
y 42 wl 
The evidence is perhaps sufficient to give the order of the genes in this 
group as Y-Pl-Sm WI. ANDERSON (1922) also notes another factor pair 
in this group. Fine-streaked leaves (fi) has been found to be linked 
with the Y factor. 
The sixth linkage group has been discovered by EMERSON (1920). It 
involves the Pp factor pair controlling pericarp color and the Ts és pair 
(normal-tassel seed plants). These factors are either very closely lin- 
ked or the two pairs are indentical. 
KEMPTON (1921c) reports that the Br br (normal-brachytic dwarf) 
factors show linkage with pericarp and cob color, very likely Pp. In 
this case there is approximately 35 per cent crossing over (range of 31 
to 43) between these factors. 
ESR 35 Br 
Nr 
VIL. 
A seventh group of factors showing linkage comprises the Aa pair 
(anthocyanin plant color) and the Vv pair (green-virescent seedling 
chlorophyll). Tests reported by STROMAN (1923) indicate a very loose 



