viz. a Vignoles or flanged rail with a transverse steel sleeper formed out of a ribbed plate, with lugs or clips formed out of the solid to take the rail flange, and fastened with a steel key. In this system there is nothing that can get loose, and excellent results are obtained in India, where several millions are now in use.

In Chapter IV. we find the Midland Railway thoroughly discussed. The growth of this enterprising and pushing Company is carefully and vividly delineated. This large system, like most others, is the result of the amalgamation of many small companies, and, under an enlightened management, it has long been considered the most progressive railway in this country. The author gives a capital description of this large system, and many interesting statistics. Among the many special details, perhaps the Lickey incline on the Birmingham and Gloucester section is of most interest. On this incline, having a gradient of 1 in 37, the traffic has always been worked by locomotives, even in the days when stationary engines were used to haul the trains out of Euston Station and Lime Street Station at Liverpool; and further, in these early days (1839), the English-built locomotive was unable to be of much use on this incline, and some American locomotives were imported and succeeded in working the traffic. Derby is the "Crewe" of the Midland. Here the Company builds the locomotives, carriages, and most of the waggons. The travelling public owe much to the Midland Company. On this line the author tells us most of the new departures in rolling-stock and details were originally tried, the Pullman car and many other equally important novelties, down to the diminutive but most useful apparatus, the sand-blast, for sanding the rails under the treads of the driving-wheels of the locomotive. The effects of this apparatus are very interesting, and its use is becoming universal. So much does it add to the effectiveness of a single-wheeled locomotive that it is possible to use it on trains in place of the four-coupled engine, a saving evident to those familiar with the subject. The single-wheeled engines, running at high speeds, are more free; which means less wear and tear to the engine itself, and probably the permanent way. With an express train the sand-blast apparatus uses about nine ounces of sand per mile, giving a continuous supply to the driving-wheels; and, be the rails ever so greasy, the wheels seldom slip half a turn. The testing of the materials used at Derby Works appears to be very efficient; the steel, particularly for plates, axles, tyres, &c., being thoroughly tested by tensile and bending tests, and by chemical analysis.

Chapter V. deals with the Great Northern, NorthEastern, and Manchester, Sheffield, and Lincolnshire Railways. In any description of the Great Northern system it would be impossible to pass over the splendid running of the Company's express trains. Some of these are, without doubt, the fastest in the world. The 1051 miles between Grantham and London are continuously "done" in 117 minutes, or at the rate of 54 miles per hour; and both up and down trains are known to get over 60 consecutive miles in as many minutes. On one occasion, the author states, the 105 miles were "reeled oti" in 112 minutes-a result worthy of Mr. Stirling's splendid locomotives. The description of driving the "Flying Scot" is very true, and we are glad to observe

that the author combats the nonsense written to the daily press concerning the drivers and firemen of the Scotch expresses "being paralyzed with fear at the awful speeds." No two men are prouder of their positions, nor would they exchange into any other link. Their position is, in fact, the blue ribbon of the foot-plate.

In dealing with the North-Eastern Railway, the author gives much useful information on the subject of the compound locomotive. The locomotive superintendent of that railway, Mr. T. W. Worsdell, uses probably the best arrangement of cylinders, &c., possible to fulfil the many conditions under which a satisfactory locomotive must be constructed, and the results obtained appear to point to a great saving in fuel. We would commend to our readers the description of the snow-block on this railway in the year 1886; it is well written.

With reference to the electric lighting of trains on the Glasgow underground section of the North British Railway, it should be noted that the current is taken off the third insulated rail, not by a brush, as stated by the author, but by means of a wheel in a swing frame under each coach. This wheel runs on the central elevated and insulated rail, and each coach is electrically independent of any other. The system appears to work very well. To the Manchester, Sheffield, and Lincolnshire Railway the author gives little attention, for reasons stated on p. 193. Probably no line in this country is more handicapped by heavy gradients on its main line, and the locomotive stock has had to be designed to satisfy the conditions, more especially on the section between Manchester and Sheffield. The late Mr. Charles Sacré, the eminent engineer and locomotive superintendent of that railway, designed some particularly fine four-coupled bogie engines for the passenger service, and his goods engines did good work on the heavy sections.

The Great Western Railway loses nothing by the description given in Chapter VI. This historical line is well described, and the "battle of the gauges" thoroughly gone into. It is to be regretted that some compromise was not made between the rival gauges; for it is now evident that the four feet eight and a half inches gauge-the standard one in this country-is not wide enough. Locomotives and rolling stock have grown so much that locomotive engineers are in difficulties when trying to design more powerful engines. Take, for instance, the Indian or the Irish broad gauge; in these cases the engines are not limited in width so much, and can have ample bearing surfaces; as well as, for inside cylinder engines, crank axles not tied down by considerations of cylinder centres and the like. A ride on the "Dutchman" express locomotive is well enough described to make many young locomotive engineers long to have shared with the author that thoroughly enjoyable experience. The Severn Tunnel is well treated in this chapter. Chapter VII. deals with the South-Western Railway, and the following one gives much useful information of that model of all southern railwaysthe London, Brighton, and South Coast Railway. In noticing the latter we cannot but express our regret for the loss that Company and locomotive engineering generally have sustained by the recent death of Mr. William Stroudley. Without doubt one of our ablest railway engineers, he brought the designing of locomotives and

rolling-stock to the highest pitch; his engines are patterns to be used with advantage, and their coal consumption is the lowest on record. Chapter IX. describes the SouthEastern and Chatham Railways; and the volume concludes with Chapter X., on the Great Eastern Railway. These last chapters lack none of the interest to be found in the earlier ones in the book.

The second volume, on Scottish railways, is merely a continuation of the first, and is written in the same lucid style. Its most interesting part is a description of the Forth Bridge. Mr. Acworth gives a good account of the bridge and the earlier schemes proposed for crossing the Forth.

Mr. Acworth has written two most interesting books, which will be of great use to all in any way connected with, or interested in, the British railway system.

DISEASES OF PLANTS.

N. J. L.

Diseases of Plants. By Prof. H. Marshall Ward, F. R.S., M.A. (London: Society for Promoting Christian Knowledge.)

THIS

HIS little book is an excellent popular introduction to the study of the diseases of plants, in so far as they are due to the attacks of parasitic Fungi or similar organisms. The author, who has made this field of research especially his own, succeeds in being intelligible and interesting to ordinary readers, without in any degree sacrificing the scientific character of his work.

The book is illustrated by fifty-three woodcuts, which have been very well selected, many of them from the author's own papers. In certain cases, however, the engraving leaves something to be desired, and scarcely does justice to the original figures.

An introductory chapter explains what is here meant by disease in plants, namely "those disturbances of the structure and functions of the plant, which actually threaten the life of the plants, or at least their existence as useful objects of culture." The two factors of disease, the external cause on the one hand, and the condition of the patient on the other, are clearly distinguished.

The second chapter gives a general account of Fungi as saprophytes and parasites. Mucor is described as an example of the former, and vine-mildew (Peronospora viticola) of the latter group.

The succeeding nine chapters, forming the bulk of the book, are occupied with the consideration of special diseases.

First comes the "damping-off" of seedlings, a disease only too well known to gardeners, due to the attacks of various species of Pythium. The whole life-history of the parasite is described. In Fig. 9 it is a pity that the point of attachment of the antheridium is not more clearly shown.

Next, we have an account of the very interesting disease of cabbages and other Crucifers, known as "fingers and toes," "club-root," &c. Here the cause of the mischief is a Myxomycete, and this is the only case of a non-fungoid disease described in the book. Happily, a satisfactory cure can here be prescribed.

Chap. v. is on the potato-disease. An account of to normal mode of nutrition of the plant in health is troduced in order to show the exact nature of ta deadly injury which is wrought by the Phytophthor As a preventive measure, the selection of resist varieties of the potato is especially recommende Chap. vi. is devoted to the "smut" of corn. The cause of the frequent failure of protective dressings applied to the ripe grain is discussed. If, however, Jensen believes, the ovule may be infected at the time flowering, an altogether new light is thrown on th ļ question.

After a chapter on the disease known as "bladder plums," caused by the yeast-like Fungus Exoascus, we come to the lily-disease. The Fungus which is here responsible has been shown by Prof. Ward to afford excellent example of a saprophyte which can become a parasite on occasion.

The next three chapters describe the ergot of rye, the mildew of hop (Podosphæra), and the rust of wheat. I the case of the hop-disease, a figure of the conidia mit have been added with advantage. The now familiar b always interesting story of the heterocism of rust well told.

With a caution which in the case of a popular work cannot be too highly commended, the author avoids expressing any opinion on the subjects of fertilization !? Podosphæra, and of the function of the spermogonia in cidium.

In the concluding chapter, Prof. Ward endeavours interest his readers in the wider questions of mycolog so fascinating to the botanist, such as the phylogenet: origin and relationships of the Fungi.

The book should have a wide circulation among the numerous classes interested in the important group diseases of plants with which it deals.

OUR BOOK SHELF.

D. H. S.

The Physician as Naturalist. Addresses and Memors bearing on the History of and Progress of Medicine chiefly during the last hundred years. By W Gairdner, M.D. (Glasgow: Maclehrose and Sor. 1889.)

A SUCCESSFUL physician, during a long and busy life, frequently called upon to preside and deliver addresse at meetings at which he is expected to treat his subje in a more or less popular manner.

Dr. Gairdner has brought together a most interesting series of such addresses, which fall into two main groups First, those in which he has contrasted the treatme of the present day with that in vogue among our pr decessors of more or less remote times; and in which he has attempted to present the answer to that eveinteresting question, "Is the treatment of disease adopted at the present day superior to that in vog formerly? And if so, in what does its superiority consist: Second, those in which he lays down the lines o which he considers the medical education of the future should be conducted, in order to lead to still gres advances.

The dependence of modern treatment upon the dis cussion of accumulations of facts, and not solely upon theory, and the necessity of making experience ara

not authority the arbiter in cases of doubt, are the conclusions which the author inculcates throughout.

A century ago it was considered a fundamental principle

that venesection was essential in most, if not all, serious illnesses; and, to such an extent was this carried, that 200 ounces of blood were sometimes drawn off during i week, and even half that amount in 24 hours. Next came a reaction, and the theory that fever patients required stimulation, rather than venesection, led to the administration of enormous quantities of alcohol, especially at the hands of Dr. Todd, who at times administered more than four gallons of brandy to young girls during an illness. Finally, to Dr. Gairdner himself is due much of the credit of the modern treatment; for in 1864 he showed that in fevers, especially typhus, the mortality is far less when the patients are supported with milk and not with alcohol. Quackery and humbug meet with but urtle mercy at the author's hands, and the hollowness of the pretensions of homeopathy is well brought out in an essay contributed thirty years ago, which is reprinted in

this collection.

The volume should meet with a large circle of readers outside the medical profession, as it is eminently readble and touches upon many points in the past history of medicine as well as in modern practice, which are of *nterest to all.

Materials for a Flora of the Malayan Peninsula. Part I. By Dr. George King, F.R.S., Calcutta. Pp. 50. Reprinted from the Journal of the Asiatic Society of Bengal, 1889, No. 4)

IR J. D. HOOKER'S "Flora of British India," of which me volumes out of seven are now printed, marks an era in tropical botany, inasmuch as it will probably contain descriptions, with their synonymy, of half the tropical plants of the Old World. It furnishes, therefore, a broad platform for his successors to build upon. It is not likely that within the bounds of India proper many new plants still remain to be described; but it is not so in the wonderfully rich flora of the Malay peninsula. During The last ten years large collections have been accumulated at Calcutta from this region, gathered mainly by Scortechini and other collectors who have been sent out by the authorities of the Calcutta Botanic Garden. In the present pamphlet, which is reprinted from the Journal of the Asiatic Society of Bengal, Dr. King, the Director of the Calcutta Garden, begins a synopsis of the plants which are indigenous to the British provinces of he Malay peninsula, including the islands of Singapore, Penang, and the Nicobar and Andaman groups.

In this present paper he deals with the orders Ranuntulacer, Dilleniacea, Magnoliacea, Menispermaceæ, Nymphæacea, Capparideæ, and Violacea, leaving over the intricate and largely represented order Anonacea for another time. In these seven orders there are 35 Malayan genera and 90 species, of which 32 are here described for the first time. Amongst the novelties are included a Magnolia, a Manglietia, 3 Talaumas, an Illicium, 4 species of Capparis, and no less then 11 new Alsodeias. Besides the species here described for the first time, there are several others, known previously in Java and China, which are new to British India. It will be seen that the work will add materially to our knowledge of Indian plants, and it is to be hoped that Dr. King, in the midst of his multifarious official duties, may be able to go on with it quickly and steadily. It is hardly worth while, we think, in a series of papers of this kind, to take up space and time by recapitulating in detail the characters of the orders and genera, as, from the nature of the case, it is essentially a supplement to Hooker's "Flora of British India," in which they are already fully worked J. G. B.

out.

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE, No notice is taken of anonymous communications.]

Panmixia.

SEEING that the whole structure of Prof. Weismann's theory is founded-both logically and historically-upon the doctrine of "panmixia," and seeing that in some important respects his statement of the doctrine appears to me demonstrably erroneous, I propose to supply a paper on the subject.

It will be remembered that the principal evidence on which Mr. Darwin relied to prove the inheritance of acquired characters was that which he derived from the apparently inherited effects of use and disuse-especially as regards the bones of our domesticated animals when compared with the corresponding bones of ancestral stocks in a state of nature. Now, in all his investigations regarding this matter, the increase or decrease of a part was estimated, not by directly comparing, say, the wing bones of a domesticated duck with the wing-bones of a wild duck, but by comparing the ratio between the wing and leg bones of a tame duck with the ratio between the wing and leg bones of a wild duck. Consequently, if there be any reason to doubt the supposition that a really inherited diminution of a part thus estimated is due to the inherited effects of diminished use, such a doubt will also require to extend to the evidence of a really inherited augmentation of a part being due to the inherited effects of augmented use. Now, there is the gravest possible doubt lying against the supposition that any really inherited decrease is due to the inherited effects of disuse. For it may be-and, at any rate to a large extent, must bedue to another principle which it is remarkably strange that Mr. Darwin should have overlooked. This is the principle of what Prof. Weismann has called panmixia. If any structure which was originally built up by natural selection on account of its use, ceases any longer to be of so much use, in whatever degree it so ceases to be of use, in that degree will the premium before set upon it by natural selection be withdrawn. And the consequence of this withdrawal of selection as regards that particular part will be to allow the part in a corresponding measure to degenerate through successive generations. Weismann calls this principle panmixia, because, by such withdrawal of natural selection from any particular part, promiscuous breeding ensues with regard to that part. And it is easy to see that this principle must be one of great importance in nature, inasmuch as it must necessarily come into operation in all cases where a structure or an instinct has ceased to be useful. It is likewise easy to see that its effects --viz. of inducing degeneration-must be precisely the same as those which were attributed by Mr. Darwin to the inherited effects of disuse; and, therefore, that most of the evidence on which he relied to prove the inherited effects both of use and of disuse is vitiated by the fact that the idea of panmixia never happened to occur to him. In this connection, however, it requires to be stated that the idea first of all occurred to myself, unfortunately just after the appearance of his last edition of the "Origin of Species." I then published in these columns a somewhat detailed exposition of the subject (see NATURE, vol. ix. pp. 361, 440, vol. x. p. 164). I called the principle the cessation of selection-which still seems to me a better, because a more descriptive, term than panmixia-and at first it appeared to me, as it now appears to Weismann, entirely to supersede the necessity of supposing that the effects of use and of disuse are ever inherited in any degree at all. Thus it obviously raised the whole question touching the admissibility of the Lamarckian principles in any case, or the question which is now being so much discussed concerning the possible inheritance of acquired as distinguished from congenital characters. But Mr. Darwin satisfied me that this larger question could not be raised. That is to say, although he fully accepted the principle of panmixia, and as fully acknowledged its obvious importance, he left no doubt in my mind that there was independent evidence for the transmission of acquired characters sufficient in amount to leave the general structure of his previous theory unaffected by what he nevertheless recognized as a necessarily additional factor in it. And forasmuch as no further facts bearing upon the subject have been forthcoming since that time, I see no reason to change the judgment that was then formed.

There is, however, one respect in which Prof. Weismann's statement of the principle of panmixia differs from that which was considered by Mr. Darwin; and it is this difference of statement-which amounts to an important difference of theory-that I now wish to discuss.

The difference in question is, that while Prof. Weismann believes the cessation of selection to be capable of inducing degeneration down to the almost complete disappearance of a rudimentary organ, I have argued that, unless assisted by some other principle, it can at most only reduce the degenerating organ to considerably above one-half its original size-or probably not through so much as one-quarter. The ground of this argument (which is given in detail in the NATURE articles before alluded to) is, that panmixia depends for its action upon fortuitous variations round an ever-diminishing average-the average thus diminishing because it is no longer sustained by natural selection. But although no longer sustained by natural selection, it does continue to be sustained by heredity; and therefore, as long as the force of heredity persists unimpaired, fortuitous variations alone-or variation which is no longer controlled by natural selection-cannot reduce the dwindling organ to so much as one-half of its original size; indeed, as above foreshadowed, the balance between the positive force of heredity and the negative effects of promiscuous variability will probably be arrived at considerably above the middle line thus indicated. Only if for any reason the force of heredity begins to fail, can the average round which the cessation of selection works become a progressively diminishing average. In other words, so long as the original force of heredity as regards the useless organ remains unimpaired, the mere withdrawal of selection cannot reduce the organ much below the level of efficiency above which it was previously maintained by the presence of selection. If we take this level to be 70 per cent. of the original size, cessation of selection will reduce the organ through the 30 per cent, and there leave it fluctuating about this average, unless for any reason the force of heredity begins to fail-in which case, of course, the average will progressively fall in proportion to the progressive weakening of this force.

Now, according to my views, the force of heredity under such circumstances is always bound to fail, and this for two reasons. In the first place, it must usually happen that when an organ becomes useless, natural selection as regards that organ will not only cease, For but become reversed. the organ is now absorbing nutriment, causing weight, occupying space, and so on, uselessly. Hence, even if it be not also a source of actual danger, "economy of growth" will determine a reversal of selection against an organ which is now not merely useless, but deleterious. And this degenerating influence of the reversal of selection will throughout be assisted by the cessation of selection, which will now be always acting round a continuously sinking average. Nevertheless, a point of balance will eventually be reached in this case, just as it was in the previous case where the cessation of selection was supposed to be working alone. For, where the reversal of selection has reduced the diminishing organ to so minute a size that its presence is no longer a source of detriment to the organism, the cessation of selection will carry the reduction a small degree further; and then the organ will remain as a "rudiment.' And so it will remain permanently, unless there be some further reason why the still remaining force of heredity should be abolished. This further reason I found in the consideration that, however enduring we may suppose the force of heredity to be, it would be unreasonable to suppose that it is actually everlasting; and, therefore, that we may reasonably attribute the eventual disappearance of rudimentary organs to the eventual failure of heredity itself. In support of this view there is the fact that rudimentary organs, although very persistent, are not everlasting. That they should be very persistent is what we should expect, if the hold which heredity has upon them is great in proportion to the time during which they were originally useful, and so firmly stamped upon the organization by natural selection causing them to be strongly inherited in the first instance. Thus, for example, we might expect that it would be more difficult finally to eradicate the rudiment of a wing than the rudiment of a feather; and accordingly we find it a general rule that long-enduring rudiments are rudiments of organs distinctive of the higher taxonomic divisions-i.e. of organs which were longest in building up in the first place, and longest sustained in a state of working efficiency in the second place. Again, that rudimentary organs, although in such cases very

persistent, should not be everlasting, is also what we she? expect, unless (like Weismann) we have some argumenta reason to sustain the doctrine that the force of header. inexhaustible, so that never in any case can it become entert by a mere lapse of time-a doctrine the validity of which in 2present connection I will consider later on.

Thus, upon the whole, my view of the facts of degenera remains the same as it was when first published in these colar sixteen years ago, and may be summarized as follows.

The cessation of selection when working alone (1 probably does work in our domesticated animals, and dur the first centuries of its working upon structures or cele – which do not entail any danger to, or perceptible drain p the nutritive resources of, the organism) cannot cause degener: tion below, probably, some 20 to 30 per cent. But if fren the first the cessation of selection has been assisted by th reversal of selection (on account of the degenerating structus. having originally been of a size sufficient to entail a percepti drain on the nutritive resources of the organism, having become a source of danger, and so forth), the two pric acting together will continue to reduce the ever-dimin structure down to the point at which its presence is no kage perceptible disadvantage to the species. When that pri reached, the reversal of selection will terminate, and the ce tion of selection will not then be able of itself to reduce th organ through more than at most a very few further percentag of its original size. But, after this point has been reached, now total absence of selection, either for or against the ar will sooner or later entail this further and most importan consequence-viz. a failure of heredity as regards the g So long as the organ was of use, its efficiency was county maintained by the presence of selection-which is merely an he way of saying that selection was constantly maintaining the S of heredity as regards that organ. But as soon as the ceased to be of use, selection ceased to maintain the force of heredity; and thus, sooner or later, that force began to war. or fade. Now it is this wavering or fading of the for heredity, thus originally due to the cessation of selection, that i turn co-operates with the still continued cessation of select (panmixia) in reducing the structure below the level when reduction was left by the actual reversal of selection. So the from that level downwards the cessation of selection and the consequent failing of heredity act and react in their comm work of causing obsolescence. In the case of newly acquir characters the force of heredity will be less than in that of more anciently acquired characters; and thus we can understand z long endurance of "vestiges" characteristic of the higher taxonomic divisions, as compared with those characteristic of the lower. But in all cases, if time enough be allowed, under th cessation of selection the force of heredity will eventually fal zero, when the hitherto obsolescent structure will finally bec obsolete.1

Let us now turn to Weismann's view of degeneration. Fer of all, he has omitted to perceive that "panmixia" alote ( unassisted either by reversed selection or an inherent dimin ing of the force of heredity) cannot reduce a functionless org to the condition of a rudiment. Therefore he everywher represents panmixia (or the mere cessation of selection) as itself sufficient to cause degeneration, say from 100 to 5, instea of from 100 to 80 or 70, which, for the reasons above given, peared (and still appears) to me about the most that this princ alone can accomplish, so long as the original force of hers continues unimpaired. No doubt we have here what mu regarded as a mere oversight on the part of Prof. Weismani but the oversight is rendered remarkable by the fact that be invoke the aid of reversed selection in order to explain the f disappearance of a rudiment. Yet it is self-evident that it reversal of selection must be much more active during the me than during the final stages of degeneration, seeing tha hypothesi, the greater the degree of reduction which has bee attained the less must be the detriment arising from any uses expenditure of nutrition, &c.

And this leads me to a second oversight in Prof. Weisma statement, which is of more importance than the first. For the

It may not be needless to add that in the case of newly acquin! comparatively trivial characters, with regard to which reversal of sels for not likely to take place (eg. slight differences of colour between albe, ye?! cessation of selection is likely to be very soon assisted by a fulure to force of heredity; seeing that such newly acquired characters will it' strongly inherited as are the more ancient characters distinctive of taxonomic groups.