PHYTOGA MY. 245 



sense Is adopted, or whether the two are combined. Darwin's 

 investigation, undertaken to determine by exjjeriments whether 

 such crossing is beneficial, is published in the remainingvolume 

 of the series under consideration — that on " The Effects of 

 Cross and Self- Fertilization in the Vegetable Kingdom." It 

 does not fall within the scope and limits of this notice to set 

 forth the nature and the extent of these experiments. Readers 

 interested will go to the book, and probably have done so 

 already. As to the results we may only say that, on the whole, 

 they corroborate the inference — in some cases unequivocally 

 and strongly, in others feebly, while in a very few the result 

 was simply negative. While the crossing in many cases showed 

 astonishing reinvigoration, and self-fertilization evident injury, 

 the maximum good was obtained at the first or second cross- 

 ing ; and some close-fertilized plants soon became tolerant of 

 that condition, and retained their fertility for several close- 

 bred o-enerations. If the Darwinian thesis was on the whole 

 maintained, yet it was also shown that plants have many in- 

 explicable idiosyncrasies, and that many unknown or obscure 

 factors enter into the results of the experiment. On looking 

 over the series we are reminded of the late Jeffries Wyman's 

 aphorism : " No single experiment in physiology is worth 

 anything." 



It seems reasonably made out that the benefit of cross is, 

 ccetens paribus, in direct relation to a certain difference in 

 constitution between the two parents, or to some difference 

 in their surroundings or antecedents, from which diversity of 

 constitution may be inferred. The benefit is more decided 

 when the parents come together from a distance than when 

 grown side by side for several generations, and " a cross be- 

 tween two flowers on the same plant does no good, or very 

 little good." The qualification is a proper one. It would be 

 hasty to infer that it does absolutely no good, even though 

 the advantage be inappreciable in any single instance. Still, 

 however just and fairly well sustained the principle of Dar- 

 win's aphorism may be, it is confronted by the immense and 

 seemingly endless vitality of long-propagated varieties which 

 do not seed at all. 



