SEC. iv NAGELPS EXPERIMENT 79 



plants, all that need be said from my standpoint is, that it is 

 by no means in contradiction to my view, but rather helps to 

 confirm the correctness thereof : Nageli shows, for instance, 

 that the crossing of nearly related plants living together 

 (Hieracium species) does not, as might a priori be expected, 

 lead to the production of intermediate forms, but rather of 

 varieties which possess the characteristics of the one or the 

 other parent forms intensified a result which harmonises 

 completely with the process described by me as one-sided 

 heredity, and with the points of view indicated in that 

 description. 1 



Against Nageli's supposition that the influences of climate 

 and nutrition are of no consequence in the formation of 

 varieties, it is, however, to be -urged that isolated negative 

 examples prove nothing. This is especially the case when 

 the observations are made only on one distinct kind of 

 objects, only to a limited extent, and only during a limited 

 period of time. Such experiments prove only that in the 

 given cases the result was negative. A single positive 

 example on the other side is, however, sufficient for complete 

 proof. I have adduced here such examples, and will bring 

 forward more. Nageli's arbitrary general application of his 

 results, be it remarked in passing, is sufficient to show his 

 misuse of the word fact, and also to prove the injustice of his 

 charges against the " descriptive naturalist." 



When, therefore, this inquirer believes he has by his ex- 

 periments quite settled in the negative the question of the 

 influence of external conditions on the permanent modification 

 of species in general, and that he has shattered the whole 

 structure of the doctrine of descent hitherto held, I cannot 

 agree with him, actively as I am endeavouring myself to alter 

 that doctrine. 



1 Cf. ante p. 39, and Nageli, Das gesdlschaftliche Entstehung neuer Species, 

 Sitzungsberichte der Miinchener Akademie, 1873. 



