400 ON SUPPOSED BOTANICAL PROOFS OF [VII. 



fluences, such as nutrition, light, moisture, and that combination 

 of different influences which we call climate. All these, with 

 use and disuse, may perhaps produce great effects upon the 

 body {soma) of the individual, but cannot produce any effect 

 in the transformation of the species, simply because they can 

 never reach the germ-cells from which the succeeding genera- 

 tion arises. But if — as it seems to me — the facts of the case 

 compel us to reject the assumption of the transmission of ac- 

 quired characters, there only remains one principle by which 

 we can explain the transformation of species— the direct altera- 

 tion of the germ-plasm, however we may imagine that such 

 alterations have been produced and combined to form useful 

 modifications of the body. 



The difficulty of understanding these processes of trans- 

 formation is by no means lightened by abandoning the 

 Lamarckian theory. The difficulty in fact becomes much 

 greater, for we are now compelled to seek a different ex- 

 planation of many phenomena which were previously believed 

 to be understood. But this can hardly be regarded as a reason 

 for not accepting the view : for we are in want of a correct 

 explanation rather than one which is easy and convenient. We 

 seek truth, and when we recognize that our path is leading in 

 a wrong direction, we must leave it and take another road even 

 if it presents more difficulties. 



My theory rests, on the one hand, upon certain theoretical 

 considerations which will be mentioned below, and which I 

 have attempted to develope in previous papers \ On the other 

 hand, it rests upon the want of any actual proof of the trans- 

 mission of acquired characters. My theory might be disproved 

 in two ways, — either by actually proving that acquired cha- 

 racters are transmitted, or by showing that certain classes of 

 phenomena admit of absolutely no explanation unless such 

 characters can be transmitted. It will be admitted, however, 

 that we must be very cautious in accepting proofs of this latter 

 kind, for the impossibility of explaining a given phenomenon 

 may be merely temporar^^, and may disappear with the pro- 



^ Consult 'Ueber die Vererbung,' Jena, 1883; * Die Kontinuitat des 

 Keimplasmas,' Jena, 1885 ; ' Ueber die Zahl der Richtungskorper und 

 uber ihre Bedeutung fur die Vererbung,' Jena, 1887. These papers are 

 translated as the second, fourth and sixth Essa3^s in the present volume. 



