408 BOTANICAL BIOLOGY, 



by newer and more urgent modifications. Still, Nature is ever con- 

 servative, and these reminiscences of a bygone history persist; signifi- 

 cant to the systeoiatic botanist as telling an unmistakable family story, 

 but far removed from the stress of a struggle in which they no longer 

 are called upon to bear their part. 



Another episode in the Darwinian theory is however likely to occupy 

 our attention for some time to come. The biological world now looks 

 to Professor Weismanu as occupying the most prominent position in 

 the field of speculation. His theory of the continuity of the germ-plasm 

 has been put before English readers with extreme lucidity by Professor 

 Moseley. That theory, I am free to confess, I do not find it easy to 

 grasp clearly in all its concrete details. At any rate, my own studies 

 do not furnish me with sufficient data for criticizing them in any ad- 

 equate way. It is however bound up with another theory — then non- 

 inheritance of acquired characters — which is more open to general 

 discussion. If with Weismann we accept this principle, it can not be 

 doubted that the burden thrown on natural selection is enormously in- 

 creased. But I do not see that the theory of natural selection itself is 

 in any way impaired in consequence. 



The question however is : Are we to accept the principle ? It appears 

 to me that it is entirely a matter of evidence. It is proverbially diffi- 

 cult to prove a negative. In the analogous case of the inheritance of 

 Jiccidental mutilations, Mr. Darwin contents himself with observing 

 that we should be "cautious in denying it." Still, I believe, that though 

 a great deal of pains has been devoted to the matter, there is no case in 

 which it has been satisfactorily proved that a character acquired by an 

 organism has been transmitted to its descendants; and there is of 

 course an enormous bulk of evidence the other way. 



The consideration of this point has given rise to what has been called 

 the new Lamarckism. Now Lamarck accounted for the evolution of 

 organic nature by two principles, — the tendency to progressive advance- 

 ment and the force of external circumsta uces. The first of these prin- 

 ciples appears to me, like Niigeli's internal modifying force, t» be simply 

 substituting a name for a thing. Lamarck, like many other people 

 before him, thought that the higher organisms were derived from others 

 lower in the scale, and he explained this by saying that they had a 

 tendency to be so derived. This appears to me much as if we explained 

 the movement of a train from London to Bath by attributing it to a 

 tendency to, locomotion. Mr. Darwin lifted the whole matter out of the 

 field of mere transcendental speculation by the theory of natural 

 selection, a perfectly intelligible mechanism by which the result might 

 be brought about. Science will always prefer a material modus operandi 

 to anything so vague as the action of a tendency. 



Lamarck's second principle deserves much more serious consideration. 

 To be perfectly fair, we nuist strip it of the crude illustrations with which 

 he hampered it. To suggest that a bird became web-footed by per- 



