THE deaths of two well known explorers were announced in the Times of Saturday last. M. de Brazza died at Dakar on September 14 in his fifty-third year, and Captain J. Wiggins at Harrogate on September 13 in his seventy-fourth year. De Brazza was sent in 1875, accompanied by Dr. Ballay and M. March, naturalist, to explore the Ogowe, the great river in Gabun in Equatorial West Africa. During the succeeding eight years he laid the foundations of the French Congo Protectorate. A second visit to West Africa, which lasted for three years, was made in 1879, and during this time de Brazza persuaded King Makoko to place himself under the protection of the French flag. Successive journeys were made to the same regions in 1883 and 1887. After an expedition in 1891-2 from Brazzaville to the Upper Sungha with the view of opening up a route to the Shari and Lake Chad, de Brazza settled down in France. Last April he was sent out as commissioner to inquire into the charges of maladministration in French Congo territory, but the hardships incident to travel in the malarial tropics of Africa this time proved fatal. To Captain Joseph Wiggins belongs the credit of having discovered, or at least rediscovered, thirty years ago a new ocean highway within the Arctic circle by which the trade of European Russia obtained for the first time direct maritime access to the navigable rivers of Siberia. Captain Wiggins Fellow of the Royal Geographical Society.

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THE thirteenth annual exhibition of the Photographic Salon is now open at the Gallery of the Royal Society of Painters in Water Colours, Pall Mall East. It contains many very fine examples of photography which will interest the scientific student in showing what can be done by means of modern methods. The aim of the promoters of the exhibition is purely pictorial, and although presumably all the works shown are produced by photographic means, it is obvious that there is some, and in a few cases probably a great deal of hand-work in addition. This detracts to a certain extent from the value of the representations of the various phases of nature, of which there are several interesting examples. The methods employed are quite outside the consideration of the society responsible for the show; we can therefore only surmise that the majority of the multi-coloured pictures, and there are about a dozen of them, are made by the gumbichromate process, applying from two to five coatings of different colours as desired. But the portrait of Frederick Hollyer by Mr. F. T. Hollyer is probably printed on platinum paper, the colours being obtained by modifications in the method of development or by subsequent treatment of the print. A picture so made is obviously not a platinum print, and its permanency and other characteristics must depend entirely upon the nature of the pigmentary materials present. We do not notice any example of "photography in natural colours" as this phrase is commonly understood.

THE greater part of the Naturwissenschaftliche Wochenschrift for August 27 is devoted to a review, by Dr. Thesing, of the pathogenic protozoa, dealing particularly with the subject of syphilis.

THE Popular Science Monthly for September contains many interesting articles. Messrs. Foulk and Earhart

discuss State university salaries, and deplore the meagre remuneration of university teachers. If this be the case in America, how much more so is it in this country?

WITH reference to the article on The Sterilisation of Water in the Field" (August 31, p. 431), the Lawrence Patent Water Softener and Steriliser Company writes to say that a mistake was made in the records of the official trials of water sterilisers, and that the Lawrence steriliser never consumes more than 1 pints of kerosine per hour, not 2 pints as stated.

THE Psychological Bulletin for August (ii., No. 8) contains an Prof. important review by Dr. Meyer of Wernicke's monograph on aphasia, together with an obituary notice of Prof. Wernicke, who was killed on June 15 in a bicycle accident. We would suggest that the Bulletin be issued with cut pages in future.

THE Revue de l'École d'Anthropologie de Paris for August contains an article by MM. Capitan and Papillault on the identification of the body of Paul Jones 113 years after death. This was based partly on general characters, colour of the hair, &c., partly on measurements compared with those of certain contemporary busts, between which there was an extraordinary agreement, and partly on pathological details. There were clear indications broncho-pneumonia, of tuberculosis, and of renal disease, and from contemporary records it is known that Paul Jones suffered from all of these.

of

LIEUT. CHRISTOPHERS, I.M.S., records a discovery of considerable interest, viz. the presence of a parasite belonging to the hæmogregarines in blood of the Indian field rat (Gerbillus indicus). Hitherto it has been believed that these parasites are confined to cold-blooded vertebrates. The parasite occurs as a motionless vermicule in the red blood cells, and as an actively motile vermicule in the plasma. Infection of the rat was proved to take place through its parasitic louse, a new species of Hæmatopinus, in which a developmental cycle is passed (Sc. Mem. of the Gov. of India, No. 18).

WE have received from the director of the Government Zoological Gardens at Giza, near Cairo, a list of a collection of animals obtained by the members of the staff during a collecting trip to the Sudan, which lasted from May 10 until August 10. The list comprises 129 animals referable to 46 species, among which a pair of Senegal storks are perhaps the most notable. It should be added that several of the specimens are the gifts of officials in the Sudan, and that a giraffe was confided to the care of the director by the Khedive.

To the first part of vol. ix. of the Biological Bulletin Dr. J. E. Duerden contributes a sixth instalment of his account of the morphology of the Madreporaria, dealing in this instance with the "fossula " of the extinct rugose corals. The fossula (of which there may be several), we may remind our readers, is a very characteristic feature of the Rugosa, and consists of a pit in the calice due to the smaller size of the vertical septa in that particular area. In this communication the author endeavours to explain the structure of this pit from the changes which take place in the corallite during development.

Is the August number of Naturen Mr. H. Schetelig describes, with illustrations, certain very interesting remains of buildings of Neolithic age which have recently been opened up in Scandinavia. The building takes the form of a portion of a curved wall situated in a stratum below the peat, which is itself overlain by a considerable

thickness of more recent deposits. Alongside the wall were found a number of stone implements, most of which are of the well known Neolithic adze type, although others are chiefly finished by chipping, and appear in some degree transitional between Palæo- and Neo-lithic types.

In the first article of the August issue of the American Naturalist Prof. D. P. Penhallow discusses the ancestry of the poplars and willows (Salicaceae) as deduced from the woody structure of the fully mature stem. The family appears to be of Old World origin, and while most of its Cretaceous representatives appear to have been suited to a warm climate, the tendency of the later forms appears to have been to adapt themselves to boreal conditions. The other articles include the seventh part of Dr. B. M. Davis's studies on the plant-cell, and a dissertation by Mr. J. A. Cushman on the developmental history of the shelled foraminifera of the group Lagenidæ. For the initial chamber of these lagenoids the author proposes the name 'proloculum," on the analogy of protoconch in the case of the gastropod shell.

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THE trustees of the British Museum have caused to be issued (at the price of 3d.) a special guide to an exhibition of old natural history books now placed in the main hall of the Natural History Museum in Cromwell Road. The object of the series is to illustrate the origin and progress of the study of natural history previous to Linnean times. Apart from reproductions of certain prehistoric sketches, which scarcely, it seems to us, come under the designation of "old natural history books," the series commences with Aristotle's natural history, followed by other works collectively assigned to the classical period. Arab philosophers, such as Serapion of the eight or ninth century, come next, and following these, after a brief reference to a few mediæval writers, we are introduced to the works of Leonardo da Vinci and the early "herbalists." With the close of the fifteenth century the legendary period of natural history gave place to an era of first-hand investigation, and special reference is made in the guide to Wotton (1492-1555), the first English physician to make a scientific study of the subject, and to whom belongs the credit of restoring zoology to the rank of a science. For the history of later writers and their works we must refer our readers to the exhibition itself, which, if studied by the aid of the excellent little guide before us, cannot fail to prove both interesting and instructive.

UNDER the conditions which prevail, it is too much to expect any great expansion of forest areas in the British Isles, but there is some consolation in the statement made by Mr. G. Pinchot, the energetic chief of the Bureau of Forestry in the United States, that the Canadian and Cape Colonies have established an efficient forest service, and that Australia and New Zealand are making progress in the same direction. Mr. Pinchot reviews the conditions of forestry in Germany, France, and Switzerland, also in British India and the United States, in the August number of the National Geographic Magazine. Among the illustrations are some depicting the employment of elephants in the teak trade of Burma.

AN account of the Erysiphacea of Japan in the Annales Mycologici, vol. iii., No. 3, by Mr. E. S. Salmon, affords some instances of distribution which are not readily explained. Four species were previously only known from America, one each from Australia and China, and five are endemic. One species, Uncinula geniculata, was gathered near Tokio on an endemic plant, Styrax Obassia; as

recorded from America, the only host-plant is Morus rubra Mr. Salmon suggests that possibly Morus rubra will be found to exist in Japan, or that the area of distribution of the two host-plants may have overlapped, or that the fungus, having been introduced to Japan, has spread to a new host-plant.

THE sixteenth annual report of the Missouri Botanical Garden contains three papers on fungal diseases observed on cauliflowers by Dr. H. von Schrenck and Mr. G G. Hedgcock. Following upon the treatment of the cauliflower leaves with different fungicides, it was noticed that swellings were raised in certain cases; further experiments proved that these were caused by the application of a solution of copper ammonium carbonate which induced Prof. extravagant enlargement of the mesophyll cells. Sorauer, who has treated the subject of intumescences very fully, has referred their formation to the action of an abnormal elevation of temperature, combined with excessive water supply. In the experiments here detailed these conditions did not obtain, and Dr. Schrenck shows definitely that the swellings are the result of chemical stimulation brought about by the copper ammonium salt when applied in a dilute solution, and he compares it with the well known action of poisonous salts, which in weak solutions induce acceleration of growth.

THE August number of the Fortnightly Review contains an article by Mr. W. H. Mallock on the two attacks on science. The two attacks are the clerical and the philosophic, and the writer contends that the former of these has failed entirely, because man and the universe, when studied as modern science studies them, neither can have, nor require to have, any other explanation than that which science offers us, the principle, namely, that all phenomena result from a single system of interconnected causes. There are no longer gaps in which the divine interference can be seen, for even the gap between the organic and the mental has been bridged over by the discovery that consciousness and mind are by no means co-extensive and identical, i.e. that consciousness is not essential to the existence and operations of mind. As for the philosophic attack, the main problem is that of the origin of ideas, and Mr. Mallock accepts the scientific view that the mind is a highly complex organism, having a long pedigree, and evolved from simpler elements; that the "connection of things" gradually reproduces itself in the "connection of ideas"; that the individual is at no point to be regarded as separated from the cosmic whole, but that even conation. which has sometimes been supposed to differentiate mental from other processes, depends on the universal conation of nature. On these lines science extends indefinitely the borders of what we call self, and breaks down the dividing line between ourselves and the universe; and thus intrespective philosophy instead of disintegrating science as a system of childish materialism, merely hardens are sublimates it into a system of universal mentalism."

WE have received an effective relief map of the Dominion of Canada, on a scale of 100 miles to an inch, published by the Department of the Interior.

A RECENT Bulletin (No. 15) of the Geological Commission of Finland contains a series of chemical analyses of nineone igneous rocks from Finland and the Kola peninsula The analyses are set out and the rocks classified acording to the elaborate new method of the American petra graphers (Whitman Cross, Iddings, Pirsson, and Washing ton), in whose work many of these analyses have already appeared. Thirty-eight, however, are new, being mostly the work of Miss N. Sahlbom.

THE Geological Survey continues its work of unravelling the complex structure of the Highlands, and has lately published a memoir on the region of the Upper Tay and Tummel valleys (Sheet 55. Blair Atholl, Pitlochry, and Aberfeldy), a region where the newest and the oldest of geological formations alone are found. Most of the memoir is occupied with the field relations and petrography of the crystalline schists and igneous intrusions, but glacial and alluvial deposits are also described. Chief among the illustrations are seven very fine photographic plates. One of the most interesting is a view of the rocky bed of the Garry, with the curious" water-pipe" structure, due to unsymmetrical folds in the Moine gneiss. An example of the practical utility of the survey is given in the fact that the basalt quarries near Aberfeldy, which supply the best road-metal in the district, were started at the suggestion of a survey officer.

THE Geological Survey of Ireland has recently been transferred from the charge of the Board of Education to the Department of Agriculture and Technical Instruction, and in connection with the transference an interesting article describing the survey's history and work has been contributed by Prof. Grenville A. J. Cole to the department's journal. In this article mention is made of the fact that so long ago as 1837 a laboratory for the examination of soils was established in Belfast, and a soil survey was projected. Unfortunately, however, the authorities were unsympathetic, and Ireland has not the credit of the first soil survey. "It was left," writes Prof. Cole, "for Germany, the United States, Japan and other countries to develop agricultural geology as a branch of organised research." Under the care of Sir Horace Plunket's vigorous department, it is safe to predict that the survey will now make amends to Irish agriculture for the neglect of 1837.

WE have received the report of the United States Geological Survey on the results of primary triangulation and primary traverse for the fiscal year 1903-4, by Mr. S. S. Gannett. Prefixed to this is a valuable chart showing the "condition of astronomic location and primary control in the United States up to April 30, 1904.

a

nomer

STANDARD Sections for rolled iron were used first in Germany in 1879 and in the United States in 1897. In Great Britain the Engineering Standards Committee was appointed in April, 1901, by the Institution of Civil Engineers, the Institution of Mechanical Engineers, the Iron and Steel Institute, and the Institution of Naval Architects to inquire into the advisability of standardising rolled iron and steel sections for structural purposes; and although the time has not yet been sufficient for the standard sections to be adopted as widely as they are in Germany, the committee has done admirable work, and with the support of the Institution of Electrical Engineers important developments are being made in other fields. "British The latest reports received, namely, No. 16, Standard Specifications and Tables for Telegraph Material ” (London: Crosby Lockwood and Son, 1905, price 10s. 6d. net), and No. 23, British Standards for Trolley Groove and Wire" (London: Crosby Lockwood and Son, 1905, price 18. net.), are striking examples of the wisdom displayed by the committee in not going too far in the direction of standardisation. In the case of telegraph material it is not considered necessary to issue a specification for copper wire. No attempt has been made to standardise submarine or underground tables, nor telegraphic or telephonic apparatus; and in the case of trolley wire it has not been deemed advisable to go further in the direction of standardisation than the recommendation of certain figures for the minimum tensile breaking strength for the gauges of wire in general use. No attempt is made to standardise any particular design of trolley wheel, the committee having confined itself to recommending a groove of a certain section. In short, these standard specifications are so reasonable that they cannot fail to meet with general adoption, as economy in production is ensured without any revolutionary change or any restraint on originality of design.

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Ar the last meeting of the Faraday Society (held on July 3) a paper was presented by Prof. E. Wilson upon Alternate Current Electrolysis." The author has carried out a long series of experiments with alternating currents, using various metals as electrodes, and various metal salt solutions as electrolytes. The loss or gain in weight of the electrodes during the experiments was recorded, and accurate measurements of the potential difference and of the current intensity were also made. The exact potential difference between the electrodes was obtained by use of an exploring electrode placed between the plates and a quadrant electrometer. The following metals were experimented with-lead, zinc, iron, copper, tin, and aluminium. The frequency of the alternating period, the density and character of the electrolyte, and the current intensity were varied during the experiments with each metal. results obtained are gathered together in tabular form in the original paper, and these show that the loss of weight was greatest in the case of lead in a dilute sulphuric acid solution, and least in the case of copper. The discussion on this paper has been adjourned until the meetings of the society are resumed in November next.

The

THE Cambridge University Press has just published an Baltimore index to the volume containing Lord Kelvin's Lectures on Molecular Dynamics and the Wave Theory of Light," reviewed in NATURE of May 5, 1904.

A FOURTEENTH edition of " Mineralogy," by the late Mr. Frank Rutley, has been published by Messrs. Thomas Murby and Co. The book has been revised and corrected, and a brief notice of the radio-active elements, contributed by Mr. Ernest H. Adye, has been added.

THE VARIABLE ASTEROID 1905 Q.Y.-From a telegram from Dr. Palisa to the Kiel Centralstelle, it appears that the asteroid which, on the supposition that it was a newly discovered one, was designated 1905 Q.Y., is identical with that known previously as (167) Urda. The identity is confirmed by Prof. Berberich, who writes that on August 28 the magnitude of Urda was from 0.5m. to 1.om. brighter than shown by the value given in the Jahrbuch (Astronomische Nachrichten, No. 4046).

NOVA AQUILE No. 2.-From a note in No. 4046 of the Astronomische Nachrichten, we learn that the position first given for Nova Aquila was Im. wrong in R.A. It should have read R.A. =284° 17' (=18h. 57m. 8s.) instead of 284° 2' as given, the mistake occurring in the first telegram received at Kiel.

Observing this object on September 5, Prof. Hartwig determined the position, referred to the equinox of 1905·0, as R.A. = 284° 16′ 16′′ (=18h. 57m. 5.06s.), dec. 4° 34' 50", and found the magnitude to be 10.

FRENCH OBSERVATIONS OF THE TOTAL SOLAR ECLIPSE.— No. 10 (September 4) of the Comptes rendus contains the brief reports received from various French eclipse expeditions by the Académie des Sciences.

Prof. Janssen, M. Bigourdan, and MM. Stephan and Trépied, observing at Alcosebre, Sfax, and Guelma respectively, report satisfactory meteorological conditions and successful observations. At the last named place M. Bourget obtained fourteen negatives of the corona, using coloured screens. The parties at Cistierna, Burgos, and Tortosa were less fortunate, clouds interfering with, or totally preventing, observations. The measures of the ionisation of the electric field were, however, carried out throughout the eclipse by the observers at Tortosa. Similar observations were carried out, entirely according to programme and under perfect conditions, at Philippeville, and M. Nordmann, from a preliminary examination of the curves obtained, expects that some very interesting results will accrue when these are finally compared with those obtained on previous occasions. M. Salet, from the same station, reports that the polarisation of the corona was well observed, the deviation of the plane of feeble polarisation being 3°. Ten coronal radiations were photographed with a "Nicol " in front of the slit, and fifteen ultra-violet coronal radiations were photographed with the spectroscope.

From the eclipse station at Alcalá de Chisbert (Spain) M. M. Moye writes that the eclipse was observed under good conditions, and that the corona was very brilliant, the longest streamers occurring in the south and the northThe green line was very apparent. Shadow bands were well observed both before and after, but were invisible during, totality.

east.

Observations of the partial phase were made in Paris, where the times of the contacts and of the occultations of spots were recorded by several observers. Unfavourable meteorological conditions prevented the actinometric observations, which it was proposed to carry out Trappes, Bordeaux, and the Pic du Midi, from being made, but a series of good observations was obtained at Bagnères.

at

EYE-ESTIMATES OF THE TRANSITS OF JUPITER'S SPOTS.In order to determine whether his own eye-estimates of the transits of Jupiter's spots were subject to any error similar to that suspected by Schmidt, the Rev. T. E. R. Phillips has analysed his observations, which number about 140, and cover the period of seven apparitions. As a result he has arrived at the conclusion that at the beginning of each apparition, when the planet's hourangle is east, he observes the transit a little too early. Similarly, at the end of each apparition, when the hourangle is west, the transits are recorded a little too late. The explanation of this error is that it is due to the varying slant of the belts as the planet is removed from the meridian, and the consequent failure of the eye to determine correctly the position of the line which bisects the disc and is normal to the planet's equator. If this explanation is correct, the error should be of the opposite sense in the two hemispheres, but the evanescent character of the spots in the northern hemisphere has prevented Mr. Phillips from making this test. Again, if the cause suggested is the true one, this error should disappear if care be taken to keep the line joining the eyes parallel to the belts.

In No. 361 of the Observatory Mr. Phillips gives the details of his observations during each opposition since 1898, and a diagram which shows the effect of the error referred to above on the observed drift in longitude of the Great Red Spot Hollow." The hope is expressed that this may lead other observers to elucidate the matter further from their own experiences.

THE SOLAR ACTIVITY, JANUARY-JUNE.-No. 7, vol. xxxiv., of the Memorie della Società degli Spettroscopisti Italiani contains Prof. Mascari's usual summary of the solar observations made at the Catania Observatory during the first six months of the current year. A comparison of latter semestre of 1904 shows that the solar activity was the "frequencies" observed with those recorded for the much greater during the later period, but the increase was much more marked during the first quarter of this year than during the second. The daily frequencies of spots, faculæ, and prominences during the six months under discussion were 7-18, 7.12, and 3.29 respectively.

Two plates which accompany this publication show, diagrammatically, the sizes and positions of the prominences observed on the sun's limb at the observatories of Catania, Kalocsa, Odessa, Rome, and Zurich during the last quarter of 1902 and the first two months of 1903.

INSTITUTION OF MINING ENGINEERS. THE sixteenth annual general meeting of the Institution of Mining Engineers was held at Manchester on September 13, 14, 15, and 16 under the presidency of Sir Lees Knowles, M.P. The report of the council contained an expression of deep regret at the loss sustained by the death of the president, Sir Lowthian Bell. The Institu tion of Mining Engineers is a federation of seven local mining societies-the Manchester Geological and Mining Society; the Midland Counties Institution of Engineers: the Midland Institute of Mining, Civil and Mechanical Engineers; the Mining Institute of Scotland; the North of England Institute of Mining and Mechanical Engineers: the North Staffordshire Institute of Mining and Mechanical Engineers; and the South Staffordshire and East Worcestershire Institute of Mining Engineers. Since the formation of the institution in 1889, the membership has increased from 1239 to 2901 in 1905.

The first paper read was on the leading features of the Lancashire coalfield by Mr. Joseph Dickinson, formerly H.M. Chief Inspector of Mines. This paper gave a concise summary of the recent developments of the geological investigation of the coalfield. Electric power distribution was dealt with in a paper by Mr. R. L. Gamlen, in which he showed the advantages possessed by the power companies as providers of power. Mr. B. H Thwaite submitted a paper on colliery explosions in which he suggested, as a method of dealing with explosions, the installation of a series of pipes conveying a supply of oxygen and a pneumatic method of coal-dust removal. The former proposal met with much adverse criticism in

the discussion. Mr. Sydney F. Walker read a paper on earth in collieries, in which he pointed out some of the difficulties in carrying out the special rules drawn up by the departmental committee for the installation and use of electricity in mines. If earth was to be admitted into the system, the only method of carrying out the wishes of the committee was to use an uninsulated return completely enclosing the live conductor. The last paper read was by Mr. John T. Stobbs on the value of fossil Mollusca in Coal-measure stratigraphy. He expressed the opinion that Mollusca afforded the best means of correlating Coalmeasures, and considered that their neglect was due to inadequate collections in public museums, and to the fact that teachers failed to impress upon students the utility of the Mollusca as zonal indices. The Coal-measures were, he thought, comparatively neglected by the geologist, the knowledge of the Ordovician, Silurian, and Chalk systems being much more exact than that of the 3000 feet of Coalmeasures. The remaining days of the meeting were devoted to excursions to Chanters Colliery, to New Moss Colliery, to the Manchester Museum, to the works of the British Westinghouse Company and the Manchester Ship Canal, to Pendleton Colliery, and to other places of interest.

THE BRITISH ASSOCIATION.

SECTION K.

BOTANY.

OPENING ADDRESS BY HAROLD WAGER, F.R.S., H.M.I., PRESIDENT OF THE SECTION.

ON SOME PROBLEMS OF CELL STRUCTURE AND PHYSIOLOGY. Introduction.

WHEN Robert Hooke, in the early part of the seventeenth century, discovered, with the aid of his improved compound microscope, the cell structure of plants, he little thought that our ultimate knowledge of the physical and chemical processes in the living organism, of its growth and reproduction, of the problems of heredity and of the factors underlying the origin of life itself, would be in the main dependent upon a clear understanding of the structure and physiology of the cell.

Hooke's researches did not, in fact, carry him very far, and we must turn to the nearly contemporaneous works of Malpighi and Grew on the anatomy of plants for the first clear indication of the important part which cells take in the constitution of the various tissues of plants. The account they give of them is extremely interesting in the light of our present knowledge. Grew, for example, in speaking of the structure of the root, compares the parenchyma to a sponge, being a body porous, dilative, and pliable a most exquisitely fine wrought sponge. The pores are spherical and consist of an infinite mass of little cells or bladders. The sides of none of these are visibly pervious from one into another; but each is bounded within itself. They are the receptacles of liquor, which is ever lucid, and... always more thin or watery. There is no indication either in Grew's or Malpighi's works that they understood the significance of this cell structure, and it was not until the beginning of the nineteenth century, after a lapse of some 150 years, that any insight into the real nature of the cell and its functions was obtained. But then began a period of activity-associated with the names of Turpin, Meyen, Robert Brown, Purkinje, J. Müller, Henle, Valentin, and Dutrochet-which culminated in the cell theory of Schleiden and Schwann that the common basis of all animal and plant tissues is the cell, and that it is upon this elementary vital unit that all growth and development depends.

The nucleus was discovered in 1831 by Robert Brown in various tissues of the Orchidea and in some other families of the monocotyledons, as well as in some dicotyledons. He described it as a single circular areola, generally somewhat more opaque than the membrane of the cell," and more or less granular. It is very distinct and regular in form, and its granular matter is held together by a coagulated pulp not visibly granular, 1 Slightly abridged.

or, which may be considered equally probable, by an enveloping membrane. Although Robert Brown was the first to recognise the importance of the nucleus, and to give it a name, it had been seen by previous observers, and he himself mentions that he had met with indications of its presence in the works of Meyen and Purkinje, chiefly in some figures of the epidermis; in a memoir by Brogniart on the structure of leaves, and that Mr. Bauer had particularly noticed it in the cells of the stigma of Bletia tankervilliae, but had associated it with the impregnation by pollen. There are some figures by Leeuwenhoek, published in 1719, to which Prof. L. C. Miall has directed my attention, of blood-corpuscles of a fish, human epidermal cells, and the connective tissue of a lamb, in which nuclei are shown, and they had been seen by Fontana (1781) in epithelial cells, and by Cavolini (1787) in some fishes' eggs.

To Schleiden and Schwann the cell was essentially a membranous vesicle enclosing a fluid sap and a solid nucleus. They thought that it arose in contact with the nucleus as a delicate transparent vesicle which gradually increased in size and became filled with the watery sap. As soon as it was completely formed, the nucleus, having done its work, was either absorbed or cast off as a useless member, or in some cases was "found enclosed in the cell-wall, in which situation it passes through the "" So entire vital process of the cell which it has formed." far from being the most important organ of the cell, as we now consider it to be, they saw in the nucleus merely a centre of cell formation which is no longer required when the cell is formed. It was left for Hugo von Mohl to show that the mucus-like contents of the cell which he called protoplasm (1846) is the real living matter in which reside those activities which call into play the phenomena of life, and that the origin of nuclei by division from a nucleus already existing in the parent cell would possibly be found to occur very widely. Von Mohl, Nägeli, and Hofmeister all appear to have had some idea of the importance of the nucleus in cell division. Von Mohl says that the process is preceded in almost all cases by a formation of as many nuclei as there are to be compartments in the mother-cell." Hofmeister's description of it is interesting: "The membrane of the nucleus dissolves, but its substance remains in the midst of the cell; a mass of granular mucilage accumulates around it this parts, without being invested by a membrane, into two masses, and these afterwards become clothed with membranes and appear as two daughter

nuclei.

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It is, however, mainly to the researches of the last thirty years that we Owe our knowledge of the many complex cell-activities at work in living organisms, and we are still only just on the fringe of the great problems which cytology has to solve. Some of the most important of these are the origin and evolution of the nucleus, the meaning of the complex mode in which the nucleus divides, the origin and nature of the spindle figure and centrosomes, the part played by the chromosomes in the transmission of hereditary characteristics, the meaning of the phenomena accompanying fertilisation, the significance of the longitudinal division of the chromosomes and of their reduction in number in the sexual cells, and the evolution of the living substance. The satisfactory solution of these problems depends upon a clear understanding of the structure of protoplasm and its various differentiations. How far we have succeeded in obtaining this I will endeavour to show.

The Differentiation of Structure in the Cell. The essential constituent of a cell is the protoplasm. This is differentiated into two constituents, the cytoplasm and the nucleus. It is usually held that this differentiation is an essential one, and that these two constituents are present in all cells; but, as we shall see later, there is some evidence that not only are there cells with very rudimentary nuclei, but cells in which no trace of a nuclear structure can be found at all.

In addition to this primary differentiation of the cell, secondary differentiations occur, resulting in the production of organs such as chloroplasts, chromoplasts, leucoplasts, pyrenoids, and pigment spots, which have special