PLANT BREEDING 15 



fowls consisting of about one black, two blues, and 

 one white in every four. 



But though these examples of unfixable hybrids 

 are not rare, they are in a minority, and, speaking 

 generally, we can be fairly certain that a given 

 type can be made to breed true, and to perpetuate 

 its good qualities indefinitely. 



From Mendelian discovery the practical plant 

 breeder learns two lessons: 



Firstly, that he must not discard the Fi genera- 

 tion, simply because it does not give him what he 

 wants. It may be quite uninteresting from the 

 horticultural point of view, exhibiting some old- 

 fashioned or reversionary type, which is reproduced 

 because all the factors which constitute it, happen 

 to have been brought together in one individual. 



But from the appearance of this first generation 

 no guess can be made as to the properties of F2 

 (the second generation). A great deal of valuable 

 material has often been discarded by practical 

 horticulturists, simply through ignorance of the 

 Mendelian principles. The uninteresting types 

 produced through crossing, though no improvement 

 on the old and familiar varieties, would, if their 

 seed had been saved, probably have given many 

 novelties in the next generation. 



Secondly, and this practical lesson is, if anything, 

 more important: each individual plant must be 

 bred from separately. For the Mendelian dis- 

 covery does away with the old delusion that time 

 and continued selection are needed in order to 

 make a variety breed true. Purity of type depends 

 on the meeting of two gametes bearing similar 

 factors, and when two similarly-constituted gametes 



