10 
BULLETIN 1164, U. S. DEPARTMENT OF AGRICULTURE. 
Midloek furrov index is the length of the groove or furrow extending: down from 
the apex of the boll in the center of the external wall of the lock, expressed as a 
percentage of the length of the boll. The midloek furrow is present in Holdon, 
absent in Pima, 
Fiber length, graded. Owing to the great amount of labor which would have 
been involved in determining by measurement the actual average length of the 
fiber on so large a number of plants, a method of grading was employed which gave 
satisfactory comparative results. A perpendicular line was ruled off on a sheet 
of cardboard and parallel to this, on each side, a series of lines were drawn at inter- 
vals of about 3 millimeters (one-eighth inch), the first line being three-fourths of an 
inch from the central line. These lines were numbered from 1 to 9 on each side of 
the central line. The arrangement is shown in Figure 2. The seeds, with fiber 
adhering, were exposed for 30 minutes to a moist atmosphere, and the lint was then 
carefully parted on each side of the seed and was straightened out by combing. 
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Fig. 2.— Diagram showing the method used in grading the length of cotton fiber, the grade here indi- 
cated being Gi. 
The seed was placed with its longer axis over the central line and the number of 
the line on each side to which the bulk of the combed-out fibers extended was noted. 
If the right-hand fibers extended to line No. 7 and the left-hand fibers to Xo. 6, 
6.5 was taken as the value for that seed. The fiber on five seeds from each plant, 
each seed from a different boll, was measured in this manner and the average of the 
resulting values taken as representing the mean fiber length of the plant in question. 
The means as thus determined were then distributed in a series of grades of equal 
magnitude, numbered 1 to 9, and these grades were used in computing the statistical 
constants and coefficients of correlation of this character. The average grade for 
fiber length was high in Pima, low in Holdon. 
Fiber color, graded. Types were selected representing the range of variation in 
fiber color of the parental and F 2 populations, eight grades having been distinguished. 
The color grade for each plant was determined by comparing a sample of its ginned 
fiber with the types until the nearest equivalent was found. Of the parental popu- 
lations, Pima gave the higher grade for fiber color. 
