Miscellaneous. 



48 



LJULY, 1909. 



The most remarkable feature of this 

 result is that in this second generation 

 we get two apparently new forms, red 

 and blue, in addition to the purple and 

 white types with which we started. 

 Really these novelties are ouly new 

 combinations. The original purple was 

 a combination of red and blue ; and the 

 white was the combination of "absence 

 of red "with "absence of blue," if che 

 use of such expressions may be per- 

 mitted! In the rearrangement which 

 takes place at the formation of the 

 reproductive cells of the cross bred, we 

 get the new combinations red with 

 absence of blue and blue with absence of 

 red. When a pair of reproductive cells, 

 flach member of which bears one of 

 these particular combinations, unite, the 

 flowers of the resulting plant are either 

 red or blue as the case may be. 



No one can fail to recognise that the 

 possibility of thus obtaining new com- 

 binations of characters at will is of the 

 very greatest importance in horticulture 

 and stock raising— in the breeding of 

 new varieties of plants and animals. If 

 we find in distinct strains different 

 useful features not common to both, 

 we can very often take, as it were, 

 one character from one and a second 

 character from the other and combine 

 them together by cross breeding. What 

 is more, by selecting the proper indi- 

 viduals of the second generation, we 

 can at once obtain a strain which will 

 breed true to the new combination of 

 characters. It is hardly an exaggeration 

 to say that we can now deal with 

 separate useful characters as if they 

 were the different useful ingredients 

 of a pudding. We can take one useful 

 quality from one variety of wheat 

 for example, and combine it with 

 other useful qualities taken from other 

 varieties. This has actually been done on 

 a considerable scale by Professor Biffen 

 on the experimental farm of the Cam- 

 bridge University Department of Agri- 

 culture. 



One part especially of Professor Biffen's 

 work upon wheats calls for particular 

 notice on account of its great theoretical 

 and practical importance. This relates 

 to his discovery of the manner of inheri- 

 tance of immunity to certain diseases. 

 Biffen found that some strains of wheat 

 suffered terribly on his plots from the 

 attacks of the fungus disease known as 

 yellow rust ; other strains grown side by 

 side with the first proved to be perfectly 

 indifferent to this enemy. Biffen crossed 

 a diseased strain with a resistent one. 

 Next year he found that the offspring of 

 the cross were all badly diseased. There 

 is no doubt that any breeder without 

 the special knowledge possessed by the 



Professor would under these circum- 

 stances immediately have given up the 

 experiment as having failed of its 

 purpose, which was the production of 

 an immune strain. Biffen was not in 

 the least discouraged but raised a second 

 generation from the seeds of the diseased 

 plants. Next season the rows exhibited 

 a very remarkahle appearance. Among 

 a majority of brown and rusted plants 

 the minority stood out bright and green 

 and were entirely free from the pest. 

 When the plants were counted over at 

 harvest it was found that the propor- 

 tion of diseased to resistent plants was 

 very nearly 3 : I. Susceptibility and 

 immunity are in fact a pair of characters 

 exactly comparable with our case of 

 blackness and whiteness, and the im- 

 mune plants obtained in the second 

 generation constituted a pure resistent 

 strain. More than this, the original 

 immune strain was one of little value 

 to the farmer, whilst the susceptible 

 plant with which it was crossed was of 

 excellent quality in other respects. 

 Among the immune plants of the second 

 generation were found some which com- 

 bined the character of resistance to 

 disease with the good quality of the 

 susceptible parent, precisely as was to 

 be expected from our rule of the in- 

 heritance of two pairs of characters. 



Many facts which have long presented 

 an insoluble puzzle to practical breeders 

 and students of evolution alike, meet 

 with a ready and simple explanation in 

 terms of this conception of separately 

 heritable factors. We need only refer 

 to the facts of reversion or throwing 

 back to a more or less remote ancestor. 



It is well known that when a pair of 

 pigeons belonging to two distinct breeds 

 are mated together, the result is often a 

 blue bird more or less closely resembling 

 the wild rock pigeon from which all our 

 modern stocks of fancy pigeons are 

 supposed to be descended. The offspring 

 of such a cross are said to revert to the 

 ancestral type. 



The simple reappearance of the re- 

 cessive character in the second gener- 

 ation from across in the manner just 

 described, may be called a kind of 

 reversion, but the reversion is only to a 

 very near ancestor, in this case a grand- 

 parent. Wher e a very remote ancestr al 

 character makes its appearance we 

 require a different explanation. Here 

 again it will be simplest to take a 

 definite example— the one selected is 

 from Professor Bateson's work with 

 sweet peas. 



There seems to be very little doubt 

 that the original type of the cultivated 

 sweet pea was the purple. And the 



