344 



CAUSES OF VARIATION 



6. Whether the above statement is absolutely or only rela- 

 tively true, the fact is clear that living matter will often go 

 through its changes and complete its cycle of development 

 under extreme hardship. For example, in some species a blas- 

 tomere from the two- or from the four-celled stage may develop 

 into a whole (dwarf) embryo or into a half embryo, while in 

 others (ctenophore) each one of the first eight may develop into 

 a symmetrical and therefore complete individual, but lacking the 

 full normal number of swimming plates} 



7. The conclusion is unavoidable that living matter is endowed 

 with wonderful elasticity and persistence of plan, or an approxi- 

 mation to it, even under most adverse conditions, providing only 

 these conditions do not destroy life. 



And so we return to the original questions : How much of 

 what the individual is to be is due to inheritance ? How flex- 

 ible is the plan ? To what extent are modifications possible, and 

 to what extent are variations inherited ? 



Summary. In general the facts of differentiation and of regen- 

 eration, together with the persistence of an established type in 

 carrying forward inherited qualities even under most adverse 

 conditions, indicate extreme stability of living matter. 



On the other hand, the facts of acclimatization argue for the 

 alterability of protoplasm, both as to constitution and as to func- 

 tion, inclining one strongly to the belief that such alteration may 

 become more or less permanent with the organism. 



Altogether the conviction is forced upon us that the activities 

 of living matter proceed upon a plan inspired from within and 

 arising from the nature of the organization, but that this plan 

 has accommodated itself to surrounding conditions in the past 

 and is entirely competent to do so again whenever sufficient 

 occasion arises, provided only that the new demands be not too 

 sweeping or too suddenly imposed. 



These facts need to be constantly in the mind of the farmer, 

 who must be prepared for comparatively sweeping changes from 

 apparently slight causes. 



We pass now to a discussion of the question as to whether or 

 not individual modifications may be transmitted. 



1 Wilson, The Cell, p. 418. 



