428 State Boaki> ok AGiacri-TUTiK, &c. 



tion, and, when he had developed them to their utmost 

 capacity, had again operated among them cross-fertilizations, 

 and so on through a term of j^ears, occasionally crossing his 

 subjects, and always practicing upon them selection, can we 

 ^oubt but he would have obtained results which for diversity 

 and excellence it were impossible to eclipse ? 



But there is another advantage to be placed to the credit 

 of hybridism which I have not brought to light in this com- 

 parison. I allude to the fact, familiar to all breeders of ani- 

 yials as well as hybridizers of plants, that increased vigor is 

 often the direct result of crossing among individuals of a 

 variety or varieties of a species, just as surely as too close 

 intcr-breeding tends to the opposite effect. So abundant 

 concurrent testimony did Mr. Darwin find upon this point, 

 that he announced the principle that cross-fertihzation 

 between the varieties of a species is the plan of nature, and 

 is practically so universal that no hermaphrodite species con- 

 tinually self-fertilized would continue to exist. With regard 

 to this principle, Dr. Asa Gray, in a recent paper on the 

 question : " Do varieties wear out, or tend to wear out ? " 

 says : " If it be asked how the asserted principle is proved 

 or made probable, we can here merely say that the proof is 

 wholly inferential. But the infetence is drawn from such a 

 vast array of facts tliat it is well nigli irresistible. It is the 

 legitimate explanation of those arrangements in nature to 

 secure cross-fertilization in the species, either constantly or 

 occasionally, which are so general, so varied and diverse, 

 and we may add so exquisite and wonderful, that, once pro- 

 pounded, we see that it must be true." * * * « 

 How and why the union of two organisms, or generally 



