CHAPTEK VII 



CAUSES OF VARIATION 



HAVING come to the conclusion that heredity is due 

 to the unconscious memory of each cell, we next 

 have to inquire how variations arise. 



Amphimixis. This is an undoubted cause of 

 variation. It is well known that when new 

 varieties of a plant are wanted, cuttings or buddings 

 are not resorted to, but its seeds are sown ; for the 

 young plants differ much more from each other than 

 do those raised by any method of asexual reproduc- 

 tion. Dr. Warren has also shewn that the same is- 

 true in the Aphides. 29 Here also there is a slightly 

 greater fraternal resemblance between those born 

 by parthenogenesis than between the offspring of 

 sexual reproduction. But it does not appear that 

 amphimixis is a very important agent in variation ; 

 and it cannot originate anything new. 



Among the higher animals some of the young 

 resemble one parent more than the other ; but inter- 

 mediate forms are common, as is seen in the case 

 of hybrids or mongrels. In 1865 G. J. Mendel 

 published an account of a number of experiments he- 

 had made in crossing varieties of the garden pea 



29<< Nature," April 3rd, 1902. 

 123 



