1 70 THE COTTON PLANT IN EGYPT CHAP. 



mode. This result indicated correlation of big-boll and 

 big-seed, with segregation of big seed from small within 

 the group. Similarly, on dissecting for the twenty-four 

 smallest bolls, the modes were at 0*105 and 0*075. On 

 plotting the correlation diagram it was found to give 

 a value for "r" of about 0'3, but this diagram was 

 distinctly modal, the points being grouped, so that the 

 true value of "r" was probably very much higher. 



Similar dissections were made in respect of almost every 

 character available. In no case did the groups show 

 uniform seed- weight within the error of fluctuation. 

 Either the new group was evenly distributed over the 

 graph, there being no correlation, or else it moved to one 

 side. In the latter case, the group always assumed the 

 3 : 1 form. The most interesting of these for comparison 

 with the big-boll dissection was the dissection for "dis- 

 continuous habit of growth " ; the twenty plants which 

 most resemble the Upland parent in this respect did not 

 exceed 0'130, and formed two modes, one on and behind 

 0*085, the other on 0*105. Again, though classification 

 according to habit of branching showed no marked shift- 

 ing of the group-centre, yet the " unbranched " plants 

 filled up the 0*120 mode, while "freely branched" 

 occupied the mode at 0140 (Fig. 69). 



Two general conclusions result from this analysis. 

 Firstly, that the modes in the F 2 curve are genuine, and 

 largely due to autogenous fluctuation. 



Secondly, that the F 2 curve consists of superposed 

 curves having the 3 : 1 form, but mutually obscurant until 

 groups of comparable individuals are taken. 



Thus we have shown that light seed is segregating from 

 heavy seed in F 2 , probably as a simple pair of allelo- 

 morphs, just as in the Afifi x Truitt series. The only 

 serious weakness of this view lies in the fact that both 

 the parents were light-seeded ! The Upland parent, how- 

 ever, bore these light seeds inside a boll of 32 mm. 



