,8,,. DR. W EI SM ANN'S THEORY OF HEREDITY. 183 



Similarly a weak or tender constitution may be strengthened by 

 crossing with a more robust one, &c., so that the effect is not to 

 lower the standard of tlie whole of the offspring (as if the weaker one 

 were prepotent), but the superior strength of the healthy parent 

 raises them up to its own standard, and obliterates the downward 

 tendency. 



A few concluding words on the nature of proof. Dr. Weis- 

 mann says : — " My theory rests, on the one hand, upon certain 

 theoretical considerations. . . . On the other hand, it rests upon 

 the want of any actual proof of the transmission of acquired 

 characters. My theory might be disproved in two ways — either by 

 actually proving that acquired characters are transmitted, or by 

 showmg that certain classes of phenomena admit of absolutely no 

 explanation unless such characters can be transmitted " (p. 388). 



The reader will judge whether I have not sufficiently fulfilled 

 both these requirements of proof. He speaks of the belief in the 

 transmission of acquired characters being " vaguely felt." It is not 

 so with botanists. 



It is based, first, upon a deduction of identically the same kind 

 as of Geology and Astronomy, viz., the vast accumulation of coin- 

 cidences and correlations, which preclude the converse probability. 

 Indeed, Dr. Weismann recommends the use of this line of argument 

 himself, for he observes that the doctrine of evolution is based upon 

 it, so that " it may be maintained with the same degree of certainty 

 as that with which astronomy asserts that the earth moves round the 

 sun ; for a conclusion may be arrived at as safely by other methods 

 as by mathematical calculation " (p. 255). 



The deductions of geologists cannot be verified by experiment, 

 because we cannot make Nature retrace her steps and show us how 

 the Oolitic rocks were laid down, or how the Devonian fishes came 

 into existence. 



Similarly, astronomers cannot secure a portion of the sun for 

 chemical analysis, but we believe we know something of its composi- 

 tion by spectrum analysis, which furnishes a great number of 

 coincidences, but nothing more. 



With plants, howev.er, not only is the belief based on innumer- 

 able coincidences and correlations, infinitely more numerous than 

 the spectrum can furnish in the case of the sun, but experimental 

 evidence, whenever it has been tried, as with aquatic, subterranean, 

 maritime, spinescent, and hypertrophic structures, &c., as I have 

 shown, invariably corroborates, and thus verifies the deduction. 



Lastly, we must never lose sight of the fact that Dr. Weismann 

 does not pretend to offer anything more for our acceptance than an 

 "assumption" (p. 197), or a "theoretical consideration" (p. 388), 

 or an "imagination" (p. 174). He admits that no microscope has 

 ever revealed the nature, or we may add, the existence of germ-plasm, 

 or proved it to be as complicated as he assumes (pp. 168, 191, 271). 



