VARIATION AND .HEREDITY 207 



12 to 22, yet the curve of variation proved itself to 

 be a double-humped one (see cut), with one mode for 



13 florets and another for 21. De Vries rejected all 

 the flowers of the latter class, and planted the seeds 

 of the 12- and 13-rayed flowers. The result is 

 indicated in the third curve, " C " ; all the flowers 

 were of the 13-rayed variety, and the 21 -rayed plants 

 had been eliminated. The bearing of this result 

 will be discussed further on in another connection. 



FIG. 77. Discontinuous variation in Chrysanthemum segetum (see toxt). 



Mutations. Discontinuous variation may be 

 qualitative as well as quantitative. Although such 

 variations are conspicuous and striking to us, they 

 are probably of the same sort as the merely quanti- 

 tative or meristic variation. This kind of variation 

 has long been familiar to gardeners and horticul- 

 turists under the name of " sports." A classical 

 example studied under experimental conditions is 

 the evening primrose (CEnothera lamarckiana) . 

 This species is supposed to have been introduced 

 into Europe from America, although it is no longer 

 found wild here. Professor De Vries secured some 



