Inheritance of Salmon Silk Color in Maize 549 
4. The dominant A factor must be present in every individual where 
silk color separations are to be made. 
5. Aleurone color must be avoided. 
6. Presence of the dominant B factor, while not affecting accuracy, 
would nevertheless facilitate note-taking by making all the plants of 
two sharply differentiated classes, purple and sun red. 
To avoid as many as possible of these difficulties and accomplish the 
results within the shortest period of years, the following procedure was 
put into effect: Crosses were made involving the factors Y, PI, and Sm 
in different combinations. In all of these crosses, pericarp color and also 
the R factor for aleurone color were kept recessive. At the same time, an 
attempt was made to find or isolate a stock of the triple recessive of the 
desired composition. Tests of all available salmon-silk material revealed 
two closely related families breeding true for red pericarp, white endosperm, 
and recessive r. Both families consisted of sun red and dilute sun red 
plants showing the B factor to have been heterozygous. These were used 
the following year in the backcrosses. Their composition was y y pi pi s?n 
sm r r P P A A, some plants being homozygous and some heterozygous 
for dominant B. Pollen of these plants was used on silks of the Fi 
crosses. 
These backcrosses were made in 1918 and the progenies were grown in 
1919. The results are given in table 4 (page 550). The percentages of 
crossing-over are: Y-Pl, 28.9; Pl-Sm, 9.1; Y-Sm, 36.6; showing their 
relative order to be Y- Pl-Sm. 
While material for these tests was being built up, some much less satis- 
factory backcrosses were made by pollinating white-endosperm, brown- 
silked, dilute sun red plants with pollen from crosses involving F, PI, 
and Sm. These were grown in 1918. The results are given in table 5 
(page 551). 
A summary of the percentages of crossing-over is given in table 6 
(page 552). 
The chromosome map 
From the totals of all the data obtained on these linkage relations, the 
observed percentages of crossing-over are found to be 29.70 for Y-Pl, 
10.01 for Pl-Sm, and 36.79 for Y-Sm. This shows their relative map 
order to be Y-Pl-Sm. The distance from Y to PI as observed is 29.7, 
