VARIATION 55 



from well-fertilized soil in moist hotbed conditions 

 under a weak light. 



c. Weismann, on the contrary, believes that the 

 causes of variation, at least of heritable variations, 

 are intrinsic or inborn in the germplasm. His con- 

 ception of sexual reproduction is that it is a device 

 for doubling the possible variations in the offspring 

 by the mingling of two strains of germplasm {am- 

 phimixis). By far the greater number of observa- 

 tions recorded go to substantiate this theory. 



Tower found among his potato-beetles, for exam- 

 ple, that two strains reared in the same environment 

 showed striking differences in variation, — a fact 

 necessarily due to intrinsic rather than to extrinsic 

 factors. Similar cases may be recalled by any one. 



d. Lastly, Bateson, whose work "On Materials 

 for the Study of Variation" already cited is a classic, 

 takes the agnostic attitude that it is rather futile 

 to guess at the causes of variation before the facts 

 are well in hand. He consequently discourages such 

 attempts by saying : "Inquiry into the causes of 

 variation is, in my judgment, premature." 



In conclusion, the words of Darwin written half 

 a century ago — "Our ignorance of the laws of 

 variation is profound" — may still be appropriately 

 quoted, notwithstanding the fact that in biometry 

 we have at least an excellent analytical method by 

 means of which considerable insight into variation 

 is being gained. 



