Hybridization 107 



For the purpose of this discussion it is enough to know 

 that crossing within the variety and change of stock within 

 ordinary bounds are beneficial, that the results in the two 

 cases seem to flow from essentially the same causes, and 

 that crossing and change of stock combined may give 

 better results than either one alone ; and this benefit is 

 expressed more in increased vigor and yield than in novel 

 and striking variations. These processes are much more 

 important than any mere groping after new variations, 

 as we have already said, not only because they are surer, 

 but because they are -universal and necessary means of 

 maintaining and improving both wild and cultivated 

 plants. Even after one succeeds in securing and fixing 

 the new variety, one must employ these means to a greater 

 or less extent to maintain fertility and vigor, and to keep 

 the variety true to its type. In the case of some garden 

 crops, in which many seeds are produced in each fruit and 

 in which the operation of pollination is easy, actual hand- 

 crossing from new stock now and then may be found to be 

 profitable. But in most cases the operation can be left 

 to nature, if the new stock is planted among the old. 

 Upon this point Darwin expressed himself as follows: 

 "It is a common practice with horticulturists to obtain 

 seeds from another place having a very different soil, so as 

 to avoid raising plants for a long succession of generations 

 under the same conditions ; but with all the species which 

 freely inter-crossed by the aid of the insects or the wind, it 

 would be an incomparably better plan to obtain seeds of 

 the required variety, which had been raised for some 

 generations under as different conditions as possible, and 

 sow them in alternate rows with seeds matured in the old 



