188 Segrerjation of a Quantitative Character in Beans 



But it must be noted that to give such transgressive distributions there 

 must be a positive difference in genotypical constitution between E and 

 M. Of course it could not be said at this early date that these indications 

 were reliable, but at least the indications were there and the jDroblem 

 had become enriched by the question of the cause of the transgressive 

 variation. 



The chart of the hybrids bore out and emphasised the evidence of 

 the distribution curves, for here the measurements do not merge as they 

 do in the curve for a whole row, but individual differences between the 

 plants stand out. Some of the plants with the smallest beans lay quite 

 outside the lowest limits of the E biotype, and there was an absence of 

 forms intermediate between E and M, those which one would have ex- 

 pected to be most numerous. In selecting seeds from the hybrids for 

 sowing in 1915, beans were chosen which, from their position on the chart, 

 relatively to the chart of E and M, seemed likely to prove either segre- 

 gated E forms or segregated M forms ; in addition, two of the strikingly 

 small lots and one which, alone, seemed to occupy a satisfactory inter- 

 mediate position between E and M. These will be found in the first 

 genealogical table (p. 202) marked, in 1914, with letters indicating the 

 forms to which they were thought to belong; in all, six apparently M, 

 two extremely short, the one intermediate just mentioned and the rest 

 apparently typical E. 



The harvest from these beans was as before gathered and preserved 

 plant by plant, and a sample of 25 beans taken at random from each 

 measured. The result was that in the six rows of plants whose seed had 

 been selected as M, the beans of each plant belonged to that type ; in 

 the two rows whose seed had been selected as extremely short, all the 

 plants bore seed whose distribution curves lay well to the left of the 

 control curves for E. On the charts, the M seed gave only M beans in 

 every case ; the extremely short gave only forms lying in a group to the 

 left of and higher than the E group. On the other hand, the distribu- 

 tion curves for the plants from the E seed showed the same transgressive 

 variation as the 1914 curves ; on the charts the plant averages stood out 

 sharply and clearly as segregates, some belonging to the extremely short 

 type, which we shall henceforth call X, some apparently E and some M. 



The distribution curve for the intermediate — seed from plant 46, i, 

 in 1914; row 9 in 1915 — maintained its position, and on its chart the 

 group of plants lay intermediate between the E and M groups with- 

 out any evidence of segregation such as appeared in the groups last 

 mentioned. 



i 



