MENDELISM 445 



rubbing against them. Further, if a variety is susceptible, no 

 plant of it under field conditions ever appears to escape." x 



Mr. Biffen concludes with the following remark : " Of the 

 problems this opens up to the pathologist, nothing need be said 

 here : for the present we are concerned with plant improvement, 

 and it need only be noted that, according to the report of the 

 International Phytological Bureau in 1890, the attacks of rust 

 cost Germany some £20,000,000 sterling. Such figures give one 

 some idea of the stakes the plant-breeder can now play for, and, 

 thanks to the work of Mendel, with the reasonable certainty of 

 winning." 



But it is not merely by the discovery of facts of this kind 

 that Mendelism is of service to the breeder of animals and plants. 



Mendel and his followers have already put into the hands of 

 breeders general principles of the greatest value. For example, 

 those whose business is to breed cattle or carnations, or whose 

 hobby is to breed fancy mice or sweet peas, and strive to 

 improve their strains by crossing, are likely to be disappointed 

 if they expect anything new in their first crosses. What could 

 be more discouraging than to obtain a house mouse by crossing 

 the delicate little waltzing mouse with the albino ? And yet I 

 have raised an entirely new colour — lilac, as it is called — by 

 mating these hybrids together. Similarly in sweet peas the 

 production of the original wild type of that flower by crossing 

 two of the most beautiful modern strains would not tempt one to 

 repeat the experiment. Mendelian principles drive home the 

 lesson that we must expect nothing in the way of novelty from 

 the first generation, and that it is on the next one that we must 

 concentrate our attention. 



Another extremely valuable instrument which Mendel has 

 put into the hand of the breeder is the power of effecting the 

 combination in one strain of desirable characters existing in 

 separate strains, with great swiftness and precision. If the two 

 characters we wish to combine are recessive ones, our task is an 

 easy one, for we can effect their association in 1 individual in 

 every 16 in the F2 generation. If, however, it is a dominant one, 

 we have to wait till the following generation in order to deter- 

 mine which of the individuals bearing the dominant character 

 are heterozygotes and which homozygotes. 



1 Royal Horticultural Society, Third International Conference on Genetics, 

 P. 376. 



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