THE PLASTICITY OF LIFE 209 



There are several similar sets of facts in regard to plants, 

 and their elaboration is one of the most urgent and promising 

 of evolutionist inquiries. It is probable that we are here 

 on the track of discovering what may be called external 

 variational stimuli, and it may be that along this line of 

 experiment will be found an interpretation of some cases 

 suggestive of the transmission of modifications, which 

 is, for many reasons, highly improbable and, in any case, 

 unproved. It gives a fresh interest to the seasonal out- 

 look, too, to reflect that this complex and changeful environ- 

 ment, through which so many plants and animals, in spite 

 of all that we have said of their modifiability, pass callously 

 and unaffected, may yet be not without its influence on 

 generations yet unborn. 



All naturalists are agreed in admitting that modifica- 

 tions are very common, that they are of much individual 

 importance, that they may have an indirect influence 

 through the parent's body on the offspring (especially 

 in the case of mammalian mothers), and that they may 

 have in various ways an indirect importance in evolution ; 

 but there is less agreement as to the answer to be given 

 to the following much-debated and often misunderstood 

 question : Does a structural change in the body, induced 

 by change of function, or by change in surroundings and 

 nurture generally, ever influence the germ-plasm in the 

 reproductive organs in such a specific or representative 

 way that the offspring will thereby exhibit the same modi- 

 fication that the parent acquired, or even a tendency 

 towards it ? For our part, we do not know of any clear 

 case which would at present warrant the assertion that a 

 bodily modification is ever transmitted from parent to 

 offspring. 



What is certain, however, is that the plasticity of the 

 living creature admits of definite modifications being 



