204 BREEDING 



theory already described, and partly on de Vries' 

 work, referred to in Chapter I. These new prin- 

 ciples of breeding, together with an account of an 

 experiment carried out to test their truth, will form 

 the subject of Chapter XV. 



But whilst the value of the theory enunciated 

 in the last chapter is of this indirect nature, the 

 theory to be described in this, which is merely an 

 extension of the first-named, is of immediate practical 

 value, inasmuch as a familiarity with it greatly 

 increases the facility with which one of the most 

 important methods of the breeder, the combination, 

 in one strain, of characters existing in distinct strains, 

 can be carried out. 



The two methods of the breeder are, first, the 

 method of selection, which alters and improves the 

 characters of breeds ; and, secondly, the method of 

 hybridisation which merely effects the recombination 

 of characters which are not themselves altered. And 

 it may be said that the theory to account for the 

 results which follow a cross involving a single pair 

 of characters, described in the last chapter, throws 

 an indirect light on the first of these methods ; whilst 

 the theory to account for the results which follow 

 a cross involving two pairs of characters, to be 

 described in this chapter, directly facilitates the 

 second of these methods. 



These preliminary remarks are intended to indicate, 

 roughly, the application of the theory which has 

 been, and that which is about to be, dealt with. 

 Both of them, of course, have other applications as 



