CHARACTERS IX AX UPLAXD-EGYPTIAX COTTOX HYBRID. 27 
curve may have been a result of insufficiently accurate grading, the 
difference between any two successive grades having been slight. 
Assuming that two modes actually occurred, a vers' close approxima- 
tion to a 3 to 1 ratio is obtained by grouping together as " yellow ; ' 
those individuals whose pollen equaled or surpassed in intensity of 
color that of the first generation (grades 4 to 6) and grouping as 
"pale" the individuals which had lighter colored pollen than Fj 
(grades 2 and 3). The numbers in the two classes are 156 and 59, 
while the expectation would have been approximately 161 and 54. 
On the assumption that both absence of the petal spot and pale 
color of the anthers are simple Mendelian recessives, 1 individual in 
16 should have presented this combination. The actual number 
was 15 in an F 2 population of 215. or 1 in 14.3. The departure from 
the expected ratio was not significant. 
MIDLOCK FURROW INDEX. 
Indication of segregation in a definite ratio is afforded also by 
the character midfoek furrow (fig. 37), which was present in the 
Holdon parental population and absent in the Pima parental popu- 
lation and in F v Examination of the boll photographs showed that 
the presence or absence of the midlock furrow could be determined 
definitely in 181 F 2 individuals, of which 94 showed no trace of the 
furrow, while in the remaining 87 plants it was present in varying 
degrees. On the basis of a 9 to 7 dihybrid ratio, assuming absence 
of the furrow to result from the combination of two dominant factors, 
the proportion of individuals without furrow should have been 56 
per cent. The actual percentage having been 52 ±2.5, the departure 
from the expected ratio was not significant. 
DATA OF THE HOLDON-PIMA HYBRID COMPARED WITH EVIDENCE 
FROM OTHER SOURCES OF MENDELIAN SEGREGATION IN COTTON 
HYBRIDS. 
Cotton hybrids have been studied from a Mendelian point of view 
by Balls, Fletcher, Fyson, Harland, Leake, Leake and Prasad, 
McLendon, and Shoemaker. It is in order to consider the evidence 
of definite segregation obtained by these investigators, especially in 
regard to characters determined on the upland-Egyptian hybrid 
which is the subject of this bulletin. 
LEAF SHAPE. 
_ Two expressions of leaf shape were the subject of investigation in the Holdon- 
Pima hybrid. These were leaf index (width as a percentage of the length) and leaf- 
lobe index (distance to the upper sinus as a percentage of the length), this beiiu r an 
expression of the depth of lobation. The mean leaf index of F x was higher than that 
of either parental population, the leaves having been relatively as well as absolutely 
wider than in Pima. The mean leaf lobe index of F T was almost exactly the same 
as that of Pima, the more deeply lobed parent. In F._, the curves representing the 
frequency distributions for both indices resemble normal frequency curves (figs. 10 
and 11), indicating that several factors are involved in each of these characters : 
Similar, but not identical, leaf characters studied by others have shown evidence of 
more definite segregation. 
Leake (30, pp. 14, 15) devised an expression of leaf shape which he termed the 
"leaf factor" and which integrates the breadth of the lobes and the depth of the 
lobation. 20 His data indicate that in crosses of Gossupium indicum, which has a 
»The leaf factor i^ the length of the midvein irinus the distance to the upper sinus divided by the 
maximum width of the terminal lote. 
