14 The Significance of Horticultural Varieties. 



Hence the illusion of an increase in Tariahility. The ex- 

 planation is simply this that, as shown in the preceding 

 section (§ 1), we first find a minus variant of the new 

 character, which, in accordance with the law of regres- 

 sion, approaches not tlie cliaracter of the old species but 

 the mean value of the new variety, as soon as it is iso- 

 lated. And this takes place easily and swiftly since the 

 new variety in this case behaves like an improved race 

 on the cessation of selection or under reversed selection 

 (Vol 1, ^ 14, p. 122). 



The progress made by this improvement and through 

 the purification from the results of crossing is often so 

 rapid that it can be expressed in terms of a geometrical 

 series. This generalization does not attain to the rank 

 of a law, but my meaning will become clearer by citing 

 an example. Hofmeister sowed the seeds of plants of 

 Papaver soniniferuni polycephaluni} which he had found 

 growing between normal examples of the species. By 

 selecting the fruits which were richest in supernumerarv 

 carpels, but without isolation, he effected the following- 

 increase in the number of abnormal examples in the suc- 

 ceeding generations : 



These figures, as we see, do not differ considerably 

 from a geometric series. I do not lay much stress on 

 the fact, but I have myself more than once obtained 

 similar series of figures in breeding experiments. 



The limits that can be reached are as little under the 

 control of the l^'eeder as the starting-points that had to 



"^ All gem cine Morphologic, p. 565. See our Fig. 27 on p. 13S of 

 the first volume; also Hoffmann, Bof. Zcifg., 1881, p. 397, and Ver- 

 LOT, Production ct fixation dcs varictcs, p. 88. 



