298 Practical Application [ch. 



Mendelian discovery at once abolishes the old delusion 

 that time and continued selection are needed in order to 

 make a variety breed true ; for the homozygous individuals, 

 which are the only ones that will breed true, may appear 

 in F^, It is the business of the breeder to find such indi- 

 viduals. By continued selection he may perhaps succeed 

 ultimately, for at each selection he somewhat increases 

 his chance of finding them, but by following Mendelian 

 method he can go straight to the desired end, obviating 

 many years' work. 



. Unfixable Types. 



There are of course certain types which cannot be fixed 

 at all, for the reason that their special character is not 

 represented in their gametes, but is a special consequence 

 of the meeting of dissimilar gametes. In animals the Anda- 

 lusian fowl is a case in point. 



The colours of Canaries are mostly of this class, and 

 in order to obtain the requisite shades of yellow various 

 crosses between pure coloured varieties are made, scarcely 

 any being bred pure for exhibition. The '* Golden Duck- 

 wing " of Game fowls is another heterozygous colour, and 

 can be produced by crossing Silver Duckwing with Black- 

 red. The only structural feature of this kind that I can name 

 is the crest of the crested Canaries, which is always bred 

 for shows by mating cresteds with plain-headed birds (R.E.C., 

 19 ; Davenport, 105). The admired crest consists of long, 

 drooping feathers radiating symmetrically from the top of 

 the head in one of several approved patterns. This neatly- 

 laid appearance is only produced when the bird is hetero- 

 zygous for the crest-factor. 



Among plants there are doubtless many examples'^. For 

 instance, among their pedigree strains of Primula Shiensis 

 Messrs Sutton have met with two which are clearly of this 

 nature. One is a large-flowered type known as '' Giant 

 Lavender," having a pale magenta flower. This never 

 comes true from seed, throwing always a number of bright 

 magenta-reds, and a corresponding number of whites more 



* Compare Baur's case of Antirrhinum (p. 253), which Hke many other 

 variegated plants proved unfixable because it is a heterozygous type. 



