SYSTEMATIC IMPROVEMENT OF PLANTS 20 1 



that is, we are unable to discriminate between the pure D 2 and 

 the 2 Dr with its unnoticeable recessive, r. How, now, shall 

 these be separated ? 



It is a long and difficult process. The only procedure is to 

 plant the seeds, separately if possible. Those that are pure 

 dominants will of course produce only dominants, while those 

 that are mixed will produce both kinds ; that is, among these 

 no recessive will appear. In self-fertilizing species we can 

 quickly separate the pure dominant strains, but when it is neces- 

 sary to resort to cross fertilization, either natural or artificial, it 

 is evident that the work is still more difficult. Under such circum- 

 stances the only way is to proceed at random until a strain 

 appears that produces no recessives, when it may be confidently 

 assumed that the parents were both pure dominants and that 

 the separation has been effected. 



When more than two characters are involved. It is sufficiently 

 difficult to separate two characters, one of which is dominant. 

 Manifestly, it is still more difficult to effect separations when 

 three or more characters are involved, especially if we are con- 

 cerned with all of them. 



Of course, in practical improvement we neglect all characters 

 that do not concern us, whether they are dominant or recessive ; 

 but, on the other hand, it is seldom that we are concerned with 

 so simple a problem as the separation of a single character from 

 its recessive or dominant associations. When our problem is 

 to separate two or three such characters from their hereditary 

 entanglements, the job becomes akin to hunting for the tradi- 

 tional " needle in a haystack," because the combinations are 

 exceedingly complicated ; for we remember that the individuals 

 which are recessive as to one character may be dominant or 

 mixed as to others. 1 The only way, however, is to run it down 



1 This is why, if Jerseys and Holstein-Friesians should be crossed, some of 

 the offspring would be rich in certain Jersey characters and others in other 

 characters, either Jersey or Holstein-Friesian ; but under the law of chance not 

 once in a million times, or more perhaps, would a single animal be pure Jersey 

 with reference to all the Jersey characters. Besides this, it is more than likely 



