Hybridization 105 



degrees of crossing, as both Darwin and Wallace have 

 pointed out, and it is pertinent to this discussion to 

 endeavor to discover why this similarity exists. It is 

 well proved that crossing is good for the resulting off- 

 spring, because the difference between the parents carries 

 over new combinations of characters, or at least new 

 powers into the crosses. It is a process of revitaliza- 

 tion, and the more different the stocks in desirable 

 characters within the limits of the variety, the greater 

 may be the revitalization ; and frequently the good is of a 

 more positive kind, resulting in pronounced characters 

 which may serve as the basis for new varieties. In the 

 cross, therefore, a new combination of characters or a 

 new power fit it to live better than its parents in the 

 conditions under which they lived. 



Results from change of stock. In the case of change of 

 stock we find the reverse, which, however, amounts to the 

 same thing, that the same characters or powers fit the plant 

 to live better in conditions new to it than plants which 

 have long lived in those conditions. In either case, the 

 good comes from the fitting together of new characters or 

 powers and new environments. Plants which live during 

 many generations in one place become accustomed to the 

 place, thoroughly fitted into its conditions, and are in 

 what Spencer calls a state of equilibrium. When either 

 plant or conditions change, new adjustments must take 

 place; and the plant may find an opportunity to take 

 advantage, to expand in some direction in which it has 

 before been held back ; for plants always possess greater 

 power than they are able to express. " These rhythmical 

 actions or functions (of the organism)," writes Spencer, 



