464 THE 'EFFECTS OF CROSS- [1876. 



advantage which could not follow if reproductions were en- 

 tirely asexual. 



It is remarkable that this book, the result of eleven years 

 of experimental work, owed its origin to a chance observa- 

 tion. My father had raised two beds of Linaria vulgaris — 

 one set being the offspring of cross- and the other of self-fertili- 

 sation. These plants were grown for the sake of some obser- 

 vations on inheritance, and not with any view to cross-breed- 

 ing, and he was astonished to observe that the offspring of 

 self-fertilisation were clearly less vigorous than the others. 

 It seemed incredible to him that this result could be due to 

 a single act of self-fertilisation, and it was only in the following 

 year when precisely the same result occurred in the case of 

 a similar experiment on inheritance in Carnations, that his 

 attention was " thoroughly aroused " and that he determined 

 to make a series of experiments specially directed to the 

 question. The following letters give some account of the 

 work in question :] 



C. Darwin to Asa Gray. 



September 10, [1866?] 

 .... I have just begun a large course of experiments on 

 the germination of the seed, and on the growth of the young 

 plants when raised from a pistil fertilised by pollen from the 

 same flower, and from pollen from a distinct plant of the 

 same, or of some other variety. I have not made sufficient 

 experiments to judge certainly, but in some cases the differ- 

 ence in the growth of the young plants is highly remarkable. 

 I have taken every kind of precaution in getting seed from the 

 same plant, in germinating the seed on my own chimney- 

 piece, in planting the seedlings in the same flower-pot, and 

 under this similar treatment I have seen the young seedlings 

 from the crossed seed exactly twice as tall as the seedlings 

 from the self-fertilised seed ; both seeds having germinated 

 on same day. If I can establish this fact (but perhaps it will 

 all go to the dogs), in some fifty cases, with plants of different 



