Chap. XIII. REVEKSION. 9 



before in giving size and constitution to the breed. I ob- 

 eerved in the farmyard at Betley Hall some fowls showing a 

 strong likeness to the Malay breed, and was told by Mr. 

 Toilet that he had forty years before crossed his birds with 

 Malays; and that, though he had at first attempted to get 

 rid of this strain, he had subsequently given up the attempt 

 in despair, as the Malay character would reappear. 



This strong tendency in crossed breeds to revert has given 

 ]-ise to endless discussions in how many generations after a 

 single cross, either with a distinct breed or merely with an 

 inferior animal, the breed may be considered as pure, and free 

 from all danger of reversion. Ko one supposes that less than 

 three generations suffices, and most breeders think that six, 

 seven, or eight are necessary, and some go to still greater 

 leno-ths.^^ But neither in the case of a breed which has been 

 contaminated by a single cross, nor w^hen, in the attempt to 

 form an intermediate breed, half-bred animals have been 

 matched together during many generations, can any rule be 

 laid down how soon the tendency to reversion will be oblitera- 

 ted. It depends on the difference in the strength or pre- 

 potency of transmission in the two parent-forms, on their 

 actual amount of difference, and on the nature of the con- 

 ditions of life to which the crossed offspring are exposed. But 

 we must be careful not to confound these cases of reversion to 

 characters which were gained by a cross, with those under the 

 first class, in which characters originally common to both 

 parents, but lost at some former period, reappear ; for such 

 characters may recur after an almost indefinite number of 

 generations. 



The law of reversion is as powerful with hybrids, when 

 they are sufficiently fertile to breed together, or when they 

 are repeatedly crossed with either pure j)arent-form, as in the 

 case of mongrels. It is not necessary to give instances. 

 With plants almost every one who has worked on this sub- 

 ject, from the time of Kolreuter to the present day, has 

 insisted on this tendency. Gartner has recorded some good 

 instances; but no one has given more striking ones than 



'8 Dr. P. Lucas, ' Hered. Nat.,' * Gard. Chronicle,' 1856, p. 620. 1 

 torn. ii. pp. 314, 892: see a good could add a vast number of references, 

 practical article on the subject in but th^y would be superfluous. 



