Oct. 4, 1888] 



N.A TURE 



539 



Though likely to be of use to geologists and botanists, the 

 treatment is sufficiently popular to be intelligible to the 

 general reader. The floras of the successive geological 

 formations are treated of in turn, from the oldest rocks 

 down to comparatively recent times. The two longest 

 chapters in the book are devoted to the vegetation of the 

 Devonian and Carboniferous ages respectively, much of 

 the matter here traversed having formed the subject of 

 numerous scientific memoirs by the author. In the body 

 of the work, accounts of the morphology and minute 

 anatomy of the various plant-remains are given, with 

 speculations as to their affinities, and in many cases 

 restorations are attempted, illustrated by figures. The 

 more special details as to classification, &c, are wisely 

 placed in small type as a series of notes at the end of each 

 chapter. The last chapter in the book consists of an 

 interesting essay on the general laws of origin and migra- 

 tions of plants. Many of the woodcuts leave much to be 

 desired, more especially those dealing with histological 

 subjects. These are, for the most part, scrappy and 

 insufficiently described, and convey little to the mind. 

 Comparisons between fossil remains and recent plants 

 are often rendered valueless by strange inaccuracies as to 

 the morphological value of the parts so compared. Thus 

 the leaves of Marsilca (pp. 60 and 67) are described as 

 being in whorls and cuneate in form, and in Aaolla and 

 Salvinia the leaves are " frondose and more or less pin- 

 nate in their arrangement." SpenopJiyllum, which pos- 

 sesses wedge-shaped leaves arranged in verticels on the 

 stem, is set down as of probable Rhizocarpian affinity, on 

 this mistaken comparison between its leaves and the 

 leaflets r>i Mar silea ! Much confusion also arises from a 

 careless use of the terms sporocarp, sporangium, macro- 

 and micro-spore, antheridium, &c, in connection with 

 certain small bodies found in the Erian and Carboniferous 

 beds, and conceived by the author to be the reproductive 

 bodies of a rich, then-existing Rhizocarpian flora. Though 

 there are many points in which palasobotanists may not 

 be at one with the author — such as the reference of so 

 many Palaeozoic forms to Rhizocarps — the volume will be 

 of service, especially to those to whom the larger treatises 

 are not available. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he nuder- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other fart 

 of Nature. No notice is taken of anonymous communi- 

 cations.] 



Prophetic Germs. 



I have but just returned from abroad, and have hastened to 

 read the number of Nature for August 30. I find that the 

 Duke of Argyll in his letter of that date makes some remarks 

 which call for a few words from me. The Duke is not, 

 it appears, prepared to defend the theory that the electric 

 organ of Kaia ladiata is a " prophetic germ." He refers me 

 to the paper of Prof. Ewart on this subject, whose opinion he 

 quotes and accepts. I am not sure how far Prof. Ewart himself 

 had considered the significance of the view which he put forward 

 in regard to the nature of the rudimentary electric organs of 

 skates ; but I do not hesitate to say that there are no facts which 

 have been made known at present, either by earlier observers or 

 by Trof. Ewart, with regard to the electric organ of skatts, which 

 necessitate such a theory of prophetic germs as that imagined by 

 the Duke of Argyll, or which can be shown to be inconsistent 

 with the doctrine of progressive development by the natural 

 selection of fortuitous congenital variations. If the Duke of 

 Argyll will point out such facts, he will have made a contribu- 

 tion of some value towards the understanding of the laws of 

 organic evolution. 



In a subsequent portion of his letter the Duke of Argyll 

 states: "If Prof. Ray Lankester will explain how 'natural 

 selection' can act upon 'congenital variations,' which he calls 



' non-significant' — i.e. which are not yet of any actual use — and 

 if he will explain how this action can afford ' the single and 

 sufficient theory of the origin ' of (as yet) useless variations, 

 he will have accomplished a great triumph in logic and 

 philosophy." 



I am unwilling to entertain the notion that the Duke of Argyll 

 has intentionally constructed the above sentence by garbled quota- 

 tions from my previous letter in order to produce the false 

 impression that 1 have maintained such a view as to the action 

 of natural selection. At the same time, I will observe that the 

 method of discussion adopted by the Duke — namely, that of 

 half quoting the opinion which he attributes to an opponent and 

 desires to render illogical in the judgment of otl er-s — is, to say 

 the least of it, objectionable. It becomes easy when this method 

 of partial re-stateir,ent is adopted for the disputant to insert 

 words of his own mixed with the words of his opponent, and 

 thus to misrepresent the latter's statement by unconsciously 

 fabricating what the poet has condemned as the worst of 

 fabrications — namely, one which is half a truth. 



The point of the sentence which I have above quoted from 

 the Duke of Argyll's letter depends upon the unwarrantable 

 introduction on his part after the quotation of the word "non- 

 significant " of certain words in explanation of that word. The 

 Duke is kind enough to say that by "non-significant" I mean 

 " which are not yet of any actual use." 1 have not had any 

 private communications with the Duke of Argyll upon this 

 matter, and am at a 1 66 to understand how he should have come 

 to think that he knows that this was what I meant by the word 

 "non-significant." Py whatever process he arrived at that 

 conclusion I regret to have to say that it is absolutely erroneous. 

 My meaning was nothing of the kind, and I was under the 

 impression that I had stated with sufficient clearness what 

 my meaning was. It appears that I did not state it clearly 

 enough for all readers. I called the congenital variation 

 which survives in the struggle for existence " non-significant" in 

 regard to its origin and not in regard to its survival. It was, I 

 think, clear to most readers that 1 was distinguishing between 

 the Lamarckian theory of variation as due to the transmission of 

 parental acquired characters and the Darwinian theory of varia- 

 tion as due to a "shaking up " of the germ-plasma at the union 

 of egg-cell and sperm-cell. The variation — that is, the departure 

 of a young animal or plant from the normal character of the 

 species — would be, if it could be traced to the transmission 

 from a parent of a character acquired by that parent in adap- 

 tation to the environment, significant ; that is to say, it would 

 have significance for the adjustment of the species in its very 

 origin in the parent. On the other hand, the thousand and one 

 slight or considerable departures from the mean specific form 

 which occur in every possible direction in a brood of young fish 

 or other organisms are "non-significant." They are due to a 

 long-precedent disturbance of the germ-plasma when the form of 

 the organi-m was undeveloped. No possible reaction of adjust- 

 ment can be imagined which could produce adaptation in the 

 structure of an animal or plant developed from a germ, if it 

 be a proviso that such adaptation is to have relation to a physical 

 cause of disturbance which once acted upon the germ whilst the 

 adaptational results are to come into effective existence in the 

 developed product of the germ. Hence I am led to speak of 

 congenital variations as "non-significant" in relation to the 

 disturbing causes which produce them. 



The proposition that congenital variations are selected when 

 they are not yet of any actual use is an absurdity which the 

 Duke of Argyll had no justification whatever for suggesting as 

 likely to be defended by me, and one which he arrives at by 

 misrepresenting the meaning of the adjective " non-significant." 

 As a matter of course, some one combination of congenital 

 variations is " significant "in the sense which the Duke of Argyll 

 chooses to give to that word — a sense in which I do not employ 

 it : someone combination of congenital variations in each gener- 

 ation survives because it is "significant" in the sense of being 

 useful. It is a common fallacy to suppose that natural selection 

 is only operative in producing iicm species ; on the contrary, it is 

 never in abeyance, but is equally as active in maintaining an 

 existing form as in producing a new one. 



With regard to the origin of useless variations and the general 

 question of uselessness, it is not to be expected that your columns 

 should be given over to an exposition of the common-places of 

 Darwinism. It is to be noted, firstly, that we have no right to 

 conclude that a structure is useless to the organism in which it 

 occurs because the Duke of Argyll is unable to see in what way 



