434 The Living Plant 



of any desired variation in any given plant. Therefore his only 

 resource is to wait until the desired variation appears, which will 

 be the sooner the larger the number of plants that he deals with, 

 and the more actively he employs the devices for " breaking the 

 type." Under these conditions, it is only a question of time when 

 any desired variation that is mechanically, physically, or chem- 

 ically possible will appear, after which it can be selected and 

 intensified by the methods already described. 



Let us now illustrate, by a suppositional case, the way in which 

 man makes use of variation in improving some particular kind of 

 plant. Let us suppose that out of a race of white-flowered plants, 

 the breeder desires to develop a red-flowered variety. He knows 

 it is useless to try to turn the flowers red directly, by chemicals in 

 the soil, regulation of the light, or anything of that kind, for al- 

 though white flowers might conceivably be made red by such 

 methods, the redness would not be transmitted, and the next 

 generation would be just as white as ever. He knows that his 

 only chance of success lies in the spontaneous appearance of a 

 strain of red color, and accordingly he grows just as many plants 

 as he can possibly find space for, giving them diverse conditions 

 of soil, fertilizers, situation and cultivation, in an effort to break 

 the white type. Inevitably, sooner or later, unless, indeed, as 

 sometimes happens, there is some chemical obstacle in the con- 

 stitution of the plant, some redness will appear, faintly perhaps 

 but unmistakably, in some of the white blossoms. He then 

 isolates those plants, remorselessly destroying all the remainder, 

 and breeds them together if possible, though this is by no means 

 indispensable. From the seeds of the selected plants he raises as 

 many as he can, and amongst their flowers though some revert 

 back to whiteness, the majority are likely to show the red strain of 

 the parents, while a few (though perhaps not for another genera- 

 tion or two) will exhibit a still redder strain. The latter, of course, 

 are then selected, and bred together, and their seeds are sown as 

 before. In the resulting generation will appear fewer white 



