details, from their complexity or from their intricacy, we are ignorant.

From his study of the life-conditions of some lizards, Dr. Eimer has reached the conclusion that at any given time variations occur only in a few definite directions. These directions depend on inner constitutional causes. The variations are produced by the direct action of the environment, are always transmitted, and when accumulated, become the inner constitutional cause determining the direction in which the organism will respond to new stimuli. In old males which have been subjected for a longer time than other forms to the environment there is a tendency to the appearance of new characters. These show the direction in which species-variation is going to take place. Not only does the ontogeny repeat the phylogeny in a condensed form, but the later stages of the ontogeny are prophetic of the new phylogeny. Variation, so directed and limited, assimilation causing growth, and reproduction or discontinuous growth, are the chief laws of organic growth.

Suppose a primitive undifferentiated plasma capable of responding to stimuli of heat, light, moisture, &c. In response to the action of the environment ever slightly varied in such details, various conditions would crystallize out" of the plasma, just as from a homogeneous inorganic mass crystals form in varied groups. As the organic world continued to grow, this original differentiation would increase. With increase of complexity due to the storage in each generation of the complete effect of the environment on each stage of the phylogeny, the different directions in which forms were developing would become more different. Each new character appearing would through correlation influence the whole organism. Allow a little to natural selection and a little to the results . of sexual mingling, and the varied species, orders, and classes into which the organic world can now be divided appear as the inevitable result of its mode of growth. There is no need to search for intermediate forms: they may never have existed. As the branching of a tree is the natural consequence of its mode of growth, so is separation and isolation inevitable in the whole organic world.

The two crucial points in Dr. Eimer's theory are his view of the action of the environment and his extreme Lamarckian acceptance of the transmission of acquired characters. Probably he is correct in his supposition that the extent of the direct action of the environment has as yet been unappreciated. Many characters hitherto unexplained may come to be referred to direct action, and experiment only can determine its scope. But it is no explanation of the presence of chlorophyll to refer it with the author to the continued action of sunlight upon protoplasm. And still less is it an explanation of the difference between queen and worker bee to refer it to the difference in their food. But indeed in this latter case the refutation of the author is easy. The neuter is not a different kind of bee produced by a different kind of food. It is merely an arrested queen-a queen that has not become something else on account of a different diet, but a queen that is not quite a queen because it has not had enough to eat. That this is the true state of the case is apparent from the less specialized colonies of wasps. There the queen in spring lays female eggs, and has herself to forage

for the whole brood. As a result the young do not get enough to eat, and the development of their sexual organs is arrested. They in turn help to feed the next brood, the individuals of which reach a further state of development. As the summer wears on, the ever-increasing band of workers bring in an increasing supply of food, till finally a condition is reached when there is enough food to make perfect females of a whole brood. Clearly the bee colony, with its sharper distinction between neuter and queen, is merely a specialization of this condition. It is but a verbal explanation of the difference between queen and neuter to refer it to the direct action of food upon the organism. Moreover, to explain the condition of things even in the wasp colony, natural selection is necessary. Obviously, insufficient food would arrest general development as well as sexual development, and natural selection acting on variations naturally arising had to select those whose genitalia suffered most with least detriment to general powers. From the many interesting cases adduced by the author, this one has been selected because it is fairly typical of the slight grounds on which he refers important characters to the direct action of the physical environment.

As for the inheritance of acquired characters, it may be said at once that Dr. Eimer has added nothing of importance to the controversy. He certainly has adduced a few isolated cases that seem to be explained best on this theory; and were the inheritance of acquired characters merely of incidental value to his argument, his easy acceptance of the traditional view might avoid criticism. But when it is said that the direct action of the environment, together with inner constitutional causes, produces varieties and species, and that these inner constitutional causes that determine the direction of variation are merely a summation of direct action, a summation effected by inheritance, we perceive at once that a new and all-important rôle is assigned to heredity. There is no attempt to meet the serious theoretical difficulties involved in every conception of the mechanism of the inheritance of acquired characters: there is no adequate attempt to establish the fact. Were it possible and were it true, undoubtedly it would be, as Dr. Eimer in elaborate and learned detail has shown, of immense importance. But to prove its possibility or truth Dr. Eimer has done little or nothing.

Dr. Eimer appears to have mistaken a generalized expression of the process of evolution for an explanation of it. Natural selection acts at a time only on the one or two characters which the environment temporarily elevates into criteria of existence. But, as these change, there are changed with them a vast multitude of minor characters-in a word, there results what the author happily calls "kaleidoscopic variation." These changes can be referred only indirectly to selection, though they may play no inconsiderable part in determining the appearance of the organism. With all these variations are correlated variations in the results produced by the direct physical action of the environment.

Dr. Eimer has concentrated his attention on these secondary and certainly neglected changes, and his theory is a statement of their course. But he has brought forward no motive power to take the place of natural selection in determining the ruling changes; and there

The Birds of Dorsetshire: A Contribution to the Natural History of the County. By J. C. ManselPleydell, B.A., F. L.S., &c. 8vo. pp. i-xvi., 1-179. (London and Dorchester: R. H. Porter, 1888.) Notes on the Birds of Herefordshire, contributed by Members of the Woolhope Club. Collected and Arranged by the late Henry Graves Bull, M.D., &c. pp. i-xxxii., 1-274. (London and Hereford: Jakeman and Carver, 1888.)

COUNTY lists of birds are still the order of the day. First we have Mr. Mansel-Pleydell's book on the Ornithology of Dorsetshire, a very neat little volume, compiled evidently with the greatest care. The author's long acquaintance with the country and his well-known love of natural history have rendered him the most competent authority on the subject, and he has been aided by many well-known naturalists in supplying him with instances of the capture of rare birds, so that the list is a very complete one. The inevitable Great Black Woodpecker (Picus martius) of course appears, on Pulteney's authority, but no recent specimen is extant, nor is likely to be. The Pied-billed Grebe (Podilymbus podiceps), which was first recorded by ourselves as a British bird, is placed between brackets, and considered to be "extremely doubtful" by the author. All we can say is that we should not have been godfather to the specimen, to add one more doubtful species to the already overburdened British list, unless we had felt tolerably certain of its authenticity, while the fact of the specimen being immature renders its occurrence as a chance wanderer much more probable than if it had been an adult bird in breeding-plumage. The bird has ten times more claim to a place amongst our stragglers than such species as Picus medius, Pycnonotus barbatus, and dozens of others. A most interesting history is given of the celebrated swannery at Abbotsbury, with a photographic plate, in which the birds are well depicted, but the keeper's face lacks expression! Some pretty woodcuts by Mr. Lodge are interspersed in the text. The author informs us that Puffinus obscurus (p. 113) should be P. griseus.

Dr. Bull's "Birds of Herefordshire" is one of the most useful of the county lists; for it contains a complete list of British birds, with special notes on the Herefordshire species. A great deal of care has evidently been taken over this book, which is rendered more interesting by the poetical researches of the author. Mr. Phil. Robinson, when he issues a new edition of his "Poets' Birds" will certainly have to consult this work of Dr. Bull, which contains many quotations we have not seen elsewhere. R. BOWDLER SHARPE.

begin to study it if only their lessons were made easy and attractive. This was accomplished in old times by Hugh Miller, and more recently by Canon Kingsley in his charming "Town Geology"; and Mr. Lobley, in his enthusiastic preface, raises the hope that he will follow a similar course, and provide "all intelligent readers" with a simple record of the earth's history. In this respect, however, we are disappointed. The work is a condensed account of the leading geological facts and deductions, arranged much after the fashion of an ordinary text-book. Of its general accuracy and clearness we can speak with confidence; and indeed, through his long connection with the Geologists' Association, the author has had ample opportunities of qualifying himself for his task. The work, however, is more adapted for the young student who wishes to pursue the subject, than for the general reader. We fear the patience of the latter will be tried when he reads the explanations-and not always happy explanations of outcrops, anticlinals, unconformities, and outliers, for there are no diagrams to give pictorial aid. Nor is the chapter on the composition of rocks likely to prove more readable; for surely the accounts of the physical characters of minerals, and the chemical formulæ, introduce "unnecessary scientific terminology." Again, when we read of the acidic and basic rocks, of the seismic focus and the meizoseismic curve, of the "homocircle (sic) or equal-lobed tailed fishes," and of those that present a "heterocircle-tailed character," we feel that the author has not sufficiently carried out his good intentions. In the chapter on metamorphic rocks a popular account might have been given of recent researches in the Highlands, and then perhaps rarely a H. B. W.

the author would not have remarked that reversed-fault is seen."

Sound, Light, and Heat. By Thomas Dunman. Electricity and Magnetism. By the same Author. (London: Ward, Lock, and Co., 1888.)

THESE two books are revised reprints of the articles on the subjects which have already appeared in Messrs. Ward, Lock, and Co.'s well known "Universal Instructor." They have been published in their present form for the convenience of students. The work of revision and expansion has been undertaken by Mr. Chapman Jones, the death of the original author having rendered it necessary for other hands to perform this part of the work.

As might be expected, the books are of a popular character, but their value to students of elementary physics does not in the least suffer on this account. The almost entire absence of mathematical statements makes them suitable for the most elementary students.

The method of treatment is that of the orthodox textbook, and there is very little that calls for special remark. They differ mainly from other elementary text-books inasmuch as they are brought quite up to date, especially in electrical matters. The 300 diagrams which are distributed throughout the text, though not of a high order of excellence, will do much towards enlightening the minds of those who read the books.

Though not designed to suit the syllabus of any examining body, they are well adapted for students preparing for the Science and Art Department examinations.

Sea-side and Way-side. By Julia McNair Wright. (Boston: D. C. Heath and Co., 1888.)

THIS little volume is the first of a series of "Nature Readers," intended for the use of beginners in reading. As a rule, the authors of reading-books take little trouble to excite the interest of children. Their object is to bring together a number of simple sentences, and they seem to be indifferent whether the sentences express sense or nonsense. In the present series an attempt will be made to

THE GEOLOGICAL STRUCTURE OF SCANDINAVIA AND THE SCOTTISH HIGHLANDS.

TIMBER, AND SOME OF ITS DISEASES.1

an account.

geological structure of the crystalline rocks of the Highlands of Scotland and those of Scandinavia have long engaged the attention of geologists. Among the northern observers to whose labours we are largely indebted for our knowledge of the Scandinavian regions, Dr. A. E. Törnebohm has proved himself a keen and indefatigable explorer of the Swedish uplands. Many years ago he showed that above clay-slates and limestones, with recognizable Silurian fossils, there lies a great thickness of quartzites, gneisses, and schists, called by him the Seve group. In more recently studying the relations of these rock-masses, he encountered some great difficulties, of which he sent me at the time I could not pretend to solve them, but suggested, as at least a working hypothesis, that the Scandinavian structure might be fundamentally similar to that now recognized as characteristic of the North-West Highlands, where the apparent conformable superposition of a series of schists upon fossiliferous Lower Silurian strata has been produced by great terrestrial displacements, whereby the overlying rocks have been crushed and deformed, until they have assumed a new crystalline structure along the planes of movement, these stupendous changes having occurred at some time subsequent to the Lower Silurian period. I have recently received from Dr. Törnebohm the following letter, which he gives me leave to publish, and which will no doubt be read with interest by those who are aware of the recent progress of research in this subject :-"It will perhaps interest you to learn that your suggestion four years ago regarding the construction of our Scandinavian fjelds has turned out to be correct, at least in my opinion. My late researches have little by little driven me to the conclusion that the crystalline schists belonging to what I have called the 'Seve group' have been placed over Silurian strata by an enormous eastward thrust. I admit that I have most reluctantly come to this conclusion, knowing that it implied a horizontal thrust of enormous masses of rock for more than 100 kilometres. Such a stupendous movement of entire mountain-regions is hard to realize; but facts are stubborn things."

It will be observed that Dr. Törnebohm speaks of the movement having been towards the east, whereas in the north-west of Scotland it has been in the opposite direction. In a more recent letter, in reply to one in which I had called his attention to this difference, he says:"Though in Scotland the great thrusts are westward, in Scandinavia it is quite the reverse. Here the chief movement has been to the east or south-east. In the region of Trondhjem, indeed, there have been lesser movements towards the north-west, but these may have taken place somewhat later. At least I rather suspect this, but am not prepared positively to affirm it." I may remark that in Scotland also there are districts where the thrusts have not come from the normal direction but from the westward. In the Island of Islay, for example, I recently found the limestones and quartzites piled up by sharply-cut thrust-planes which had a general westward inclination at lower angles than the displaced strata. One of the great problems in working out the complicated geology of the Highlands is the determination of the positions and extent of such thrust-planes, and the direction in which the displaced rock-masses have been moved. There can be little doubt that much mutual help in this research will be gained by a co-operation between the field geologists who are engaged in the study of these problems in Scotland and in Scandinavia.

ARCH. GEIKIE.

VIII.

HERE is a large and important class of diseases of standing timber which start from the cortex and cambium so obviously that foresters and horticulturists, struck with the external symptoms, almost invariably term them "diseases of the bark"; and since most of them lead to the production of malformations and excrescences, often with outflowing of resinous and other fluids, a sort of rough superficial analogy to certain animal diseases has been supposed, and such terms as "canker," ""cancer," and so forth, have been applied to them.

Confining our attention to the most common and typical cases, the following general statements may be made about these diseases. They usually result from imperfect healing of small wounds, the exposed cortex and cambium being attacked by some parasitic or semiparasitic fungus, as it tries to heal over the wound. The local disturbances in growth kept up by the mycelium

FIG. 28.-Piece of tree stem affected with "canker." The injury commenced after the two inner zones of wood (1 and 2) had been developed: it extended further in successive periods of growth, as shown by the receding zones 3, 4, 5, and 6, until all the cambium and cortex was destroyed except the pieces D to D. Cam, cambium; Cor, living cortex; DD, dead tissues. At each period of growth the attempt has been made to heal over the wound, as shown by the successively receding lips.

feeding on the contents of the cells of these tissues lead to the irregular growths and hypertrophies referred to; the wounds are kept open and "sore," or even extended, and there is hardly any limit to the possibilities of damage to the timber thus exposed to a multitude of dangers.

In Fig. 28 is represented a portion of a tree stem affected with "canker": the transverse section shows the periods of growth numbered 1 to 6 from within outwards. When the stem was younger, and the cambium had already developed the zones marked 1 and 2, the cortex suffered some injury near the base of the dead twig, below the figure 1. This injury was aggravated by the ravages of fungus-mycelium, which penetrated to the cambium and destroyed it over a small area in consequence of this, the next periodic zone of wood (marked 3) is of course incomplete over the damaged area, and the cortex and cambium strive to heal over the wound by liplike callus at the margins. The healing is prevented, 1 Continued from p. 111.

however, by the mycelium, which is continually extending the area of injury: consequently the next zone of wood (4 in the figure) extends even a shorter distance round the stem, and so on with 5 and 6, the cambium being now restricted to less than half round the stem-i.e. from D to D, and the same with the living cortex. Of course the injured area extends upwards and downwards also, as shown by the lips of the healing tissue. As soon as the injury extends all round, the stem dies-it is, in fact, ringed. It is also interesting to note that the zones 4 and 5 (and the same would be true of 6 when completed) are thicker than they would have been normally: this is partly due to release from pressure, and partly to a concentrated supply of nutritive materials.

Much confusion still exists between the various cases: some of them undoubtedly are due to frost or to the intense heat of direct insolation; these are, as a rule, capable of treatment more or less simple, and can be healed up. Others, again, can only be freed from the irritating agents (which, by the bye, may be insects as well as fungi) by costly and troublesome methods.

I shall only select one case for illustration, as it is typical, and only too well known. As examples of others belonging to the same broad category, I may mention the "canker "" of apple-trees, beeches, oaks, hazels, maples, hornbeams, alders, and limes, and many others; and simply pass the remark that whatever the differences in detail in the special cases, the general phenomena and processes of reasoning are the same.

Perhaps no timber disease has caused so much consternation and difference of opinion as the "larch-disease," and even now there is far too little agreement among foresters either as to what they really mean by this term, or as to what causes the malady. The larch, like other timber-trees, is subject to the attacks of various kinds of fungi and insects, in its timber, roots, and leaves; but the well-known larch-disease, which has been spreading itself over Europe during the present century, and which has caused such costly devastation in plantations, is one of the group of cancerous diseases the outward and visible signs of which are manifested in the bark and young wood.

The appearance presented by a diseased larch-stem is shown in Fig. 29. In the earlier stages of the malady the stem shows dead, slightly sunken patches, a, of various sizes on the cortex, and the wood beneath is found to cease growing it is a fact to be noted that the dead base of a dried-up branch is commonly found in the middle of the patch. The diseased cortex is found to stick to the wood below, instead of peeling off easily with a knife. At the margins of the flattened patch, just where the dead cortex joins the normal living parts, there may frequently be seen a number of small cup-like fungus fructifications (Fig. 29, 6), each of which is white or gray on the outside, and lined with orange-yellow. These are the fruit-bodies of a discomycetous fungus called Peziza Willkommii (Htg.), and which has at various times, and by various observers, received at least four other names, which we may neglect.

In the spring or early summer, the leaves of the tree are found to turn yellow and wither on several of the twigs or branches, and a flow of resin is seen at the dead patch of cortex. If the case is a bad one, the whole branch or young tree above the diseased place may die and dry up. At the margins of the patch, the edges of the sounder cortex appear to be raised.

As the disease progresses in succeeding years, the merely flattened dead patch becomes a sunken blistered hole from which resin flows: this sinking in of the destroyed tissues is due to the up-growth of the margins of the patch, and it is noticed that the up-growing margin recedes further and further from the centre of the patch. If this goes on, the patch at length extends all round the stem or branch, and the death of all that lies above is

then soon brought about, for, since the young wood and cambium beneath the dead cortex are also destroyed, the general effect is to "ring" the tree.

To understand these symptoms better, it is necessary to examine the diseased patch more closely in its various stages. The microscope shows that the dead and dying cortex, cambium, and young wood in a small patch, contain the mycelium of the fungus which gives rise to the cup-like fructifications-Peziza Willkommii-above referred to (Fig. 30); and Hartig has proved that, if the spores of this Peziza are introduced into the cortex of a healthy living larch, the mycelium to which they give rise kills the cells of the cortex and cambium, penetrates into the young wood, and causes the development of a patch which everyone would recognize as that of the larch-disease. It is thus shown that the fungus is the immediate cause of the patch in which it is found.

The next fact which has been established is that the fungus can only infect the cortex through some wound or injury-such as a crack or puncture and cannot penetrate the sound bark, &c. Once inside, however, the mycelium extends upwards, downwards, sideways, and inwards, killing and destroying all the tissues, and so inducing the outflow of resin which is so characteristic of the disease. The much-branched, septate, colourless

hyphæ can penetrate even as far as the pith, and the destroyed tissues turn brown and dry up.

After destroying a piece of the tissues in the spring, the growth of the mycelium stops in the summer, the dead cortex dries up and sticks to the wood, and the living cortex at the margins of the patch commence to form a thick layer of cork between its living cells and the diseased area.

It is this cork-formation which gives the appearance of a raised rim around the dead patch. It has long been known that the patches dry up and cease to spread in the dry season. It should be pointed out that it is one of the most general properties of living parenchymatous tissue to form cork-cells at the boundaries of an injury: if a slice is removed from a potato, for instance, the cut surface will be found in a few days with several layers of cork-cells beneath it, and the same occurs at the cut surface of a slip, or a pruned branch,-the "callus" of tissue formed is covered with a layer of cork.

If it is remembered that the cambium and young wood are destroyed beneath the patch, it will be at once clear that in succeeding periods of growth the annual rings of wood will be deficient beneath the patch.

Next year, the cambium in the healthy parts of the stem begins to form another ring; but the fungus