84 Heredity and Eugenics 



histologist, and the biological chemist supplement each 

 other in a way that bespeaks a most hopeful future. We 

 shall discuss some results obtained by the use of the oldest 

 method, that of the garden, or, to give it the more aristo- 

 cratic name, the pedigree culture. 



This method is old, but its most important results are 

 modern. A century and a half ago Kolreuter carried out 

 the first systematic studies in plant hybridization. Through 

 them he was able to show that most reciprocal crosses are 

 identical, and therefore that the pollen grain is as essential 

 and important in determining the characters of a hybrid 

 as is the ovule. Kolreuter, of course, did not know the 

 true process of reproduction, but he came as near the truth 

 as could have been expected at the time by showing that 

 an application of 50 or 60 pollen grains was sufficient for 

 the production of over 30 seeds. 



Kolreuter, and a little later Thomas Knight, both found 

 that hybrids were in general more vigorous than either of 

 the parents; and Knight from this fact argued rejuvenation 

 by hybridization and promulgated what afterward came to 

 be known as the Knight-Darwin law. This was stated by 

 Darwin in the aphorism, "Nature abhors perpetual self- 

 fertilization." Our views on this subject, as will be shown 

 in the next chapter, must now be considerably modified; 

 nevertheless Knight partially outlined a great truth. 



One other plant breeder must be mentioned as markedly 

 in advance of his age. The elder Vilmorin in the middle of 

 the nineteenth century established a principle which has 

 not until recently been given the credit it deserves. Vil- 

 morin insisted that the only method of improving plants 

 by selection is to judge each plant by the average condition 

 of its progeny. This is Vilmorin's isolation principle and 



