270 THE SIGNIFICANCE OF SEXUAL REPRODUCTION 



are in all cases re-transformed after they have been altered by culti- 

 vation in a soil different from that^n, which they usually grow, 

 and he therefore assumed that they were true species. All these 

 experiments therefore confirm the conclusion that external influences 

 may alter the individual, but that the changes produced are not 

 transmitted to the germs, and are never hereditary. 



Nageli indeed asserts that innate individual differences do not 

 exist in plants. The differences which we find, for instance, be- 

 tween two beeches or oaks, are always, according to him, modifi- 

 cations produced by the influence of varying local conditions. But 

 it is obvious that Nageli goes too far in this respect, although it 

 may be conceded that innate individual differences in plants are 

 much more difficult to distinguish from those which are acquired, 

 than in animals. 



There is no doubt about the occurrence of innate and hereditary 

 individual characters in animals, and we may find an especially 

 interesting illustration in the case of man. The human eye can 

 with practice appreciate the most minute differences between indi- 

 vidual men, and especially differences of feature. Every one knows 

 that peculiarities of feature persist in certain families through a 

 long series of generations. I need hardly remind the reader of the 

 broad forehead of the Julii, the projecting chin of the Hapsburgs, 

 or the curved nose of the Bourbons. Hence every one can see that 

 hereditary individual characters do unquestionably exist in man. The 

 same conclusion may be affirmed with equal certainty for all our 

 domestic animals, and I do not see any reason why there should 

 be any doubt about its application to other animals and to plants. 



But now the question arises, How can we explain the presence 

 of such characters consistently with a belief in the continuity of the 

 germ-plasm, a theory which implies the rejection of the supposition 

 that acquired characters can become hereditary? How can the 

 individuals of any species come to possess various characters 

 which are undoubtedly hereditary, if all changes which are due to 

 the influence of external conditions are transient and disappear 

 with the individual in which they arose? Why is it that in- 

 dividuals are distinguished by innate characters, as well as by those 

 which I have previously called transient, and how can deep-seated 

 hereditary characters arise at all, if they are not produced by the 

 external influences to which the individual is exposed ? 



