Chap. XV. OF THE MODIFICATION OF RACES. 77 



characters. Some have gone so far as to look at it as the 

 sole cause ; hut this conclusion is disproved by the facts 

 given in the chapter on Bud-variation. The belief that 

 characters not present in either parent or in their ancestors 

 frequently originate from crossing is doubtful ; that they 

 occasionally do so is probable ; but this subject will be more 

 conveniently discussed in a future chapter on the causes of 

 Variability. 



A condensed summary of this and of the three following 

 chapters, together with some remarks on Hybridism, v/ill be 

 given in the nineteenth chapter. 



