238 PLANT-BREEDING 



evolution. Experience has taught that qualities are often 

 associated with one another by distinct laws, and that a 

 knowledge of these laws may give us a power over them, 

 greater than any man has heretofore aspired to. Even a 

 suspicion of the meaning of these laws, or an intuitive appre- 

 ciation of their work, may lead to valuable results, if it is 

 only combined with a thorough knowledge of the species in 

 question. 



Before going into the details of my subject I wish to con- 

 vince my readers of the truth of these assertions by giving 

 some noticeable illustrations. The first is an old one, the 

 second is afforded by Burbank's work, and the third is taken 

 from Nilsson's experiments in agricultural breeding. It 

 will not be necessary to go into many details, since even with- 

 out them their bearing will be clear enough. 



The common stock (Matthiola incana) is cultivated in 

 double-flowered and in single varieties. The singles are 

 pure, but the seed for the doubles is saved on single- flowered 

 specimens belonging to the same variety. From these seeds 

 about one half give double and the other half single flowering 

 plants. The doubles, however, obtain a higher price on 

 the market, and it is therefore of some interest to separate 

 and isolate them as early as possible. In France this is 

 done by children, who pick out the singles and spare the 

 doubles. This is done while the plants are ver>' young, 

 having produced a Httle stem with some small leaves, but still 

 without branches and without flower buds. It is impossible, 

 therefore, to distinguish them by these buds, but there are 

 shght differences in the color and the hairs of the leaves, 

 which separate the doubles from the singles for the expe- 

 rienced eye. These differences, however, are so very sHght 

 that it is impossible to put them into words or even to explain 

 them to the layman. No botanist, as far as I know, has 

 as yet succeeded in recognizing them, and nevertheless the 



