692 EEroRT— 1888. 



And inasmuch as Mr. Romanes is of opinion that specific differences are not ' even 

 generally ' adaptive, while those of genera are, it follows that Mr. Darwin only 

 really accounted for the origin of the latter, while for an explanation of the former 

 we must look to Mr. Romanes himself. For my part, however, 1 am altogether 

 unable to accept the premises, and therefore fail to reach the conclusion. Specific 

 differences, as we find them in plants, are for the most part indubitably adaptive, 

 while the distinctive characters of genera and of hi-jher groups are rarely so. 

 Let anyone take the numerous species of some well-characterised English genus, 

 for example Ranunculus ; he wdl find that one species is distinguished by having- 

 creeping stems, one by a tuberous root, one by floating leaves, another by drawn- 

 out submerged ones, and so on. But each possesses those common characters which 

 enable the botanist almost at a glance, notwithstanding the adaptive disguise, to 

 refer them to the common genus Ranunculus. It seems to me quite easy to see, 

 in fact, why specific characters should be usually adaptive, and generic not so. 

 Species of any large genus must, from the nature of things, find themselves exposed 

 to any but uniform conditions. They must acquire, therefore, as the very con- 

 dition of their existence, those adaptive characters which the necessities of their 

 life demand. But this rarely afiects those marks of affinity which still indicate 

 their original common origin. Probably these were themselves once adaptive, but 

 they have long been overlaid by newer and more urgent modifications. Still 

 Nature is ever conservative, and these reminiscences of a bygone history persist ; 

 significant to the systematic 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 Weiss- 

 mann as occupying the most prominent position in this 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 criticising them in any adequate 

 way. It is, however, bound up with another theory — the non-inheritance of 

 acquired characters — which is more open to general discussion. If with Weissmann 

 we accept this principle, it cannot be doubted that the burden thrown on natural 

 selection is enormously increased. 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 difficult to prove a 

 negative. In the analogous case of the inheritance of accidental 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 advancement and the force of external 

 circumstances. The first of these principles appears to me, like Nageli's internal 

 modifying force, to 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 must strip it of the crude illustrations with which he hampered 



