34 INTRODUCTION 



poisons or pigment substances may be gradually weakened in successive 

 generations, while, according to the treatment pursued, the new properties 

 may be only temporarily induced, or may be permanently fixed, in the 

 former case gradually disappearing again under normal conditions. 



External influences operate only by the changes which they induce 

 in the internal constellation to which the inherent characters of the 

 organism are due. Hence, from what has already been said it follows 

 that exciting causes of internal origin may also produce permanent 

 variations, which are then said to be spontaneous or automatic. As the 

 musical-box serves to illustrate, a change of this kind may take place 

 even when all the vital activities are perfectly normal ; but spontaneous 

 variations are more readily induced when an unusual demand is made upon 

 any particular functional activity or activities. 



Every peculiarity. which is repeated in the offspring, is an hereditary 

 characteristic. Hence it is both illogical and unjustifiable to refuse to 

 pay attention to hereditary metabolic and productive powers, as well 

 as to inherited morphological characters. As is universally the case, when- 

 ever a variation may be reproduced without the assistance of the inductive 

 actions of other living elements, some obscure internal change has taken 

 place in the protoplast. This is true, not only for a bacterium, but also for 

 an ovum, for sexual as well as asexual reproduction, since many organisms 

 capable of developing hereditary variations reproduce only asexually. 



When however inductive actions are responsible for the production 

 of a given variation, the same developmental progress and final shape 

 must always result as long as the inductive actions are repeated in 

 precisely the same manner. The specific shape of a lichen is due to 

 a definite combination of interacting inductive agencies which always 

 produce the same result. Hence, when a garden variety is propagated 

 by cuttings, it remains uncertain whether or not a cell of the primary 

 meristem, isolated from and uninfluenced by the inductive agencies with 

 which it was formerly surrounded, would or would not reproduce the 

 varietal characters in question, if it were able to form a new plant. Even 

 if such an isolated cell were able to transmit the varietal characters to 

 the plant it produced, we should still have to decide whether or not the 

 transmission of the individual characters took place in a similar manner 

 to that which, on empirical grounds, we conclude to be employed in 

 the egg-cell. Even in an isolated cell a variety of factors demands con- 

 sideration, and these appear largely to be eliminated in the ovum, for 

 everything that is not absolutely essential for the growth and main- 

 tenance of the ovum after fertilization is apparently rejected as far as 

 possible. Since in every single cell the interacting influences of the 

 parts already existent are of importance with regard to the results actually 

 produced, it follows that any special product formed in the plasma or 



