Feb. 16,1924 
Inheritance of Petal Spot in Pima Cotton 
507 
yielded a coefficient of correlation of 0.645±.024 and 123 flowers of the 
spotless class gave a coefficient of 0.307i.055. 10 
ENVIRONMENTAL REACTIONS OF THE PETAL SPOT 
There is good reason to believe that both the size and the intensity 
of color of the petal spot vary in response to variations in the physical 
environment, although this has not been tested by controlled experi¬ 
ments. Soil factors play a part, not only indirectly, by affecting the rate 
of development of the plant (p. 502) but probably in a more direct manner. 
Thus it has been observed that in Pima cotton fields the petal spot is 
less well developed where the plants are stunted than where they have 
made a normal growth, although the same stock of seed was used in plant¬ 
ing the entire field. It has been shown that a positive correlation 
exists between size of flower and development of the spot, and since the 
flowers borne by stunted plants usually are small, the comparatively 
weak development of the spot on such plants may be regarded as part 
of a general reduction caused by the unfavorable environment. 
The influence of meterological factors will be examined, first, by com¬ 
paring the means for petal spot in different years and, second, by com¬ 
paring the earlier and the later flowers produced by the same individual 
plant during the same season. 
Data given in Table I indicate that conditions in some years favor a 
more pronounced expression of the petal spot, the mean grade in both 
spotted and spotless populations, but especially the latter, having been 
notably higher in 1923 than in other years. It was pointed out, in dis¬ 
cussing the evidence for the occurrence of modifying factors, that the 
lateness of flowering of the plants in the spotless parental progenies of 
1923 may have been a factor contributing to the relatively high mean 
of that year. Yet the more pronounced development of the spot in 
1923 can not be attributed wholly to this factor, for the spotted parental 
population, in which the backward plants did not seem to have the spot 
increased as was the case in the spotless population, also gave a signifi¬ 
cantly higher mean than in previous years. Comparison of the spotless 
populations of successive years in respect to the percentages of flowers 
showing no trace of the spot gives further evidence that conditions in 
1923 favored an exceptionally high degree of expression of the spot. 
Because of the retarded growth of most of the plants in the parental 
populations of 1923, the recessive P 3 progenies, in which most of the plants 
had shown a normal rate of growth, were compared with the parental 
populations of the two preceding years. The percentages of entirely 
spotless flowers were as follows, the figures in parenthesis indicating the 
total numbers of flowers graded: 1921 (290) 43.8 per cent; 1922 (561), 
45.6 per cent; 1923 (2,826), 16.1 per cent. 
In endeavoring to ascertain whether the degree of expression of the 
petal spot differs in different periods of the same season, comparison was 
made in 1922 of the means based upon the first 5 flowers and the second 
5 flowers graded on the same individual plants. The two means were 
computed separately for 143 dominant plants and for 85 recessive plants. 
10 Corolla length and petal spot were correlated positively and significantly in a hybrid between upland 
and Egyptian cottons, the coefficient of correlation for 180 Fs plants having been 0.244±.047. The corre¬ 
lations of petal spot with 37 other characters were determined on this material and in all but two cases the 
coefficient of correlation was less than 3.5 times its probable error. The correlations in question were with 
corolla length and with calyx dentation, r in the latter case having been— .220^.048. Kearney, Thomas 
H. SEGREGATION AND CORRELATION OF CHARACTERS IN AN UPI.AND-EGYPTIAN COTTON HYBRID. U. S. 
Dept. Agr. Bui. 1164, p. 45, Table 12. 1923- 
