412 Tricotylous Races. 



over a sufficiently long period of time to justify the expec- 

 tation that a definite result would be obtained. They 

 exhibit, however, one striking difference. The mean of 

 the figures for Aniarantns is between 2 — 3%, and this 

 renders it not improbable that, if the coefficients of the 

 atavists could have been incorporated in the curve, its 

 apex would have been at 0, that is to say, that a unilateral 

 or so-called half curve would have been the result. But 

 the apex of the Scrophiilaria curve is at 12% and varies 

 amongst the individual families from 8 to 20%, indi- 

 cating thereby the possibility of an isolation of a separate 

 apex for the tricotylous specimens. 



In other words, the tricotylous half race of Aniaran- 

 tus behaves, during this long period of selection, in es- 

 sentially the same w^ay as at the beginning (table p. 407), 

 whereas Scrophiilaria behaves like other half races im- 

 proved by selection. The scheme representing the in- 

 fluence of selection on the half race of Ranunculus biil- 

 bosns scmiplcnns (Fig. 52 on page 252 of this volume) 

 would apply equally to this case. 



The explanation of this difference in behavior is per- 

 haps to be sought in the assumption that in Scrophiilaria 

 tricotyly has only been indirectly improved. I am re- 

 ferring to the case of Trifolium incarnatuiu quadrifoVmm 

 which I described above on page 239. In that case the 

 smallest seeds gave rise to the largest number of aberrant 

 seedlings. If the production of small seeds could be 

 increased by selection the number of seedlings with com- 

 pound primordial leaves would also be increased. It 

 seems possible that in Scrophiilaria similar factors were at 

 work, since the cliaracter involved need not, of course, 

 necessarily be the size of the seeds. The repeated selec- 

 tion of tricotyls would not, on this assumption lead di- 



