554 
E. G. Anderson 
From combined data of tables 4 and 5: 
Coincidence = = 0.40 
1195 x 375 
These values are entirely comparable with those listed by Weinstein 
(1918) for Drosophila. From this and the similarity of all phases of 
linkage and crossing-over, it is evident that the mechanism of crossing- 
over in maize is not strikingly different from that in Drosophila except 
in one respect. In Drosophila, crossing-over occurs in oogenesis only, 
in spermatogenesis not at all. In maize the phenomena of crossing-over 
are at least of the same order in both megasporogenesis and microsporo- 
genesis. 
Summary of linkage studies 
The factor Sm for salmon silk color is shown to be linked with the 
factor Y for yellow endosperm and the factor PI for plant and anther color. 
The relative order of these three factors is Y-Pl-Sm. 
The amount of crossing-over between Y and PI is about 30 per cent; 
between PI and Sm it is about 10 per cent. 
The observed coincidence of crossing-over in the two regions Y-Pl and 
Pl-Sm was about 0.4. 
LITERATURE CITED 
Bridges, Calvin B. A linkage variation in Drosophila. Journ. exp. 
zool. 19:1-21. 1915. 
East, E. M., and Hayes, H. K. Inheritance in maize. Connecticut 
Agr. Exp. Sta. Bui. 167:1-142. 1911. 
Emerson, R. A. Genetic correlation and spurious allelomorphism in 
maize. Nebraska Agr. Exp. Sta. Ann. rept. 24:58-90. 1911. 
A fifth pair of factors, A a, for aleurone color in maize, and 
its relation to the C c and R r pairs. Cornell Univ. Agr. Exp. Sta. 
Memoir 16:225-289. 1918. 
The genetic relations of plant colors in maize. Cornell Univ. 
Agr. Exp. Sta. Memoir 39: 1-156. 1921. 
Gowen, John Whittemore. A biometrical study of crossing over. On 
the mechanism of crossing over in the third chromosome of Droso- 
phila melanogaster. Genetics 4:205-250. 1919. 
Plough, Harold H. The effect of temperature on crossingover in 
Drosophila. Journ. exp. zool. 24:147-209. 1917. 
Weinstein, Alexander. Coincidence of crossing over in Drosophila 
melanogaster (ampelophila) . Genetics 3 : 135-172. 1918. 
Memoir 41, Lysirneter Experiments — II, the seventh preceding number in this series of publications, was 
mailed on November 16, 1921. 
