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ONE of the major classes of genetic damage produced by ionising radiations is heritable reciprocal translocation. In a series of earlier publications, Brewen and Preston1–3 demonstrated that each of several mammalian species had its own unique sensitivity to translocation induction in peripheral leukocytes and that human and marmoset leukocytes, although approximately equal in sensitivity, were twice as sensitive as mouse leukocytes. Brewen and Preston4 also reported that in the Chinese hamster and the mouse, the frequency of the translocation type analysed in the peripheral leukocytes was three to four times as high as the frequency of heritable translocations produced in spermatogonial stem cells and recovered in primary spermatocytes. As the mouse is the mammal currently used as the model for estimating man's genetic risk from mutagenic exposure, Brewen and Preston's earlier observations on germ cells should be extended to include a primate and man if possible. Here we present an extension of the interspecific and somatic against germ cell comparisons.

DURING the past thirteen years the finer detail of structure in conifer tracheids has been the subject of some controversy1,2,3,4. This has centred round the fact that when transverse sections, of conifer wood are examined between crossed Nicols three layers can be distinguished in the secondary wall of a tracheid, an outer and an inner layer which are bright, and a central layer, much thicker in late wood than the other two, which is dark. A similar behaviour is observed in cross-sections of wood fibres and is shown in the case of two isolated fibres of Nothofagus cunninghami in Fig. 1. On the basis of observations such as the run of striations in surface view, the orientation of crystals grown in the wall and the features associated with fungal attack, Bailey and his collaborators have claimed that the optical heterogeneity is due to different orientation of the cellulose ‘micelles’ in the three layers; in that while the micelles in the dark layer are orientated in a steep spiral, those in the outer and inner layers lie more or less transversely1 or, in later papers, at angles between 45° and 90° to the length of the cell3,5. The case where the micelles in the outer layer are orientated transversely and those in the middle layer longitudinally is shown diagrammatically in Fig. 2 (a). On the other hand, Preston2,4,6,7, criticizing the validity of the use of evidence obtained from swollen or otherwise distorted walls and basing his conclusions only on X-ray and optical examination of undistorted material, has maintained that the optical heterogeneity is to be explained largely by a pronounced difference in angular dispersion between the layers (Fig. 2b); and that, further, any wall layers with transverse orientation can only be present to an extent so small as to give no record on the X-ray diagrams of conifer wood7 and to cause no disturbance in the optical properties of walls in surface view7. The apparently contradictory X-ray evidence brought forward by Bailey and Berkeley3 was completely disposed of as an error in interpretation6, and it seemed at that time that the case was at last clear so far as the physical evidence went.

THE increasing preoccupation of plant physiological laboratories throughout the world with problems of growth makes it very desirable that the details of structure in the cell wall, in growing tissue, should be known as completely as possible in the condition occurring in the living tissue itself. A good deal of the discussion arising from growth studies centres around the configuration of the cell wall, and the facile generalization of the striking results of X-ray analysis in dried material to cover the condition in fresh tissue is perhaps not a priori legitimate; for it is highly improbable that the dried material, even when rewetted, can be considered with any exactitude as equivalent to the original material fresh from the plant. In point of fact, attention was directed some years ago to the implications of the fact that in bacterial cellulose the planes of 6.1 A.-spacing lie parallel to the surface of the cellulose plate only after drying1, so that the demonstration of the special orientation of dried walls of Valonia2 and Cladophora3 did not necessarily guarantee a similar orientation in fresh material.

AN attempt was made some time ago1 to relate spiral growth in sporangiophores of Phycomyces to the physical properties of the wall, and the successful semi-quantitative test of the relation proposed against the data of Castle2, as well as the more recent extension to the case of spiral grain in conifers3, makes it reasonable to assume that, oversimplified though the relation undoubtedly is, it does express spiral growth in terms of the appropriate parameters. Assuming for simplicity that the ‘fibrils’ in the wall of the growth-zone are circular in section (though this is not an essential part of the theory) it appears that the rotation of the tip of the sporangiophore, Δφ, associated with a length increase of ΔL is given by the relation

DURING the past thirty years or so, intensive investigation of cellulose by various physical methods has directed attention repeatedly to the possible existence of supermolecular units of structure ranging from ‘fibrils'1 some 0·4 µ in diameter and of indefinite length to small spherical or ellipsoidal particles of diameter up to 1·5 µ2.

WE report here a comparison of two independent techniques (high-temperature argon arc and synchrotron radiation) for the determination of vacuum ultraviolet spectral radiances. Basic agreement between the methods has previously been demonstrated at 165.7 nm by Stuck and Wende1, but we have refined the techniques to produce significant improvements in accuracy and have extended the comparison to other wavelengths.

IT is rare, even in these days of specialized studies, that circumstances permit an investigator to present a 'first book' on pioneer work in any subject. This opportunity has come to Dr. White, and he has taken full advantage in the presentation of an admirable book. In the past, text-books of, tissue culture have given the quite erroneous impression that only animal biologists have any interest in the subject or could derive anything of value from its study. Dr. White presents the case of the plant biologist, based on 457 references, with commendable force. He compresses into this relatively small volume the 'high spots' of plant tissue culture up to the present, in which he has himself played an outstanding part, and points out wide fields of interest for future research. A Handbook of Plant Tissue Culture By Dr. Philip R. White. Pp. xiv + 277. (Lancaster, Pa.: The Jaques Cattell Press, 1943.) 3.75 dollars.

IN a recent communication1 we have shown by the methods of X-ray analysis that the two closely related green algae Cladophora and Spongomorpha differ fundamentally in the submicroscopic organization of their cell walls. Whereas the cells in Cladophora filaments have walls in which the skeletal substance is a highly crystalline, well-oriented native cellulose (cellulose I), those of Spongomorpha contain a poorly crystalline, scarcely oriented modification of cellulose which might be mercerized cellulose (cellulose II) or a derivative. It was pointed out some time ago2 that the air-drying of the material, necessary for X-ray investigation, does not produce any undesirable artefacts in algae, and it was therefore concluded that the structures derived in this way could legitimately be applied to the fresh material. Even preservation in formalin or alcohol does not cause any observable change in the X-ray diagram.

IN a recent letter in NATURE1 Prof. Frey-Wyssling directs attention to the importance in cell wall studies of the angular dispersion of the constituent cellulose micelles and refers to my papers as ignoring this property. Cell wall physics is a study in which there is already much controversy, and it seems therefore a pity to give the impression of a difference of opinion where none actually exists. The question centres round the desirability of taking into account not only the parallel texture said to be typical of fibres but also the so-called 'dispersed' or 'reticul' texture present in some other cell types. So far as I am concerned, the difference between 'parallel' and 'dispersed' textures is one of degree only and actually, far from taking “... only parallel textures into account...”, I have yet to investigate a single cell in which I am convinced that this texture does occur in anything like a strict sense. In some fibres2 and wood cells3, for example, where Frey-Wyssling himself supports parallel texture, and in some collen-chyma4, my collaborators and I have shown that the angular dispersion of the cellulose micelles about the extinction direction may be considerable and is probably of importance in explaining certain optical properties of the wall. These latter papers have apparently not been available to Prof. Frey-Wyssling since his citations of my papers cease in 1939.

DURING an examination of the sieve plates of Cucurbita already briefly reported1, some observations on the structure of the secondary wall in the protoxylem have been made which seem worth recording.

Atlas of Electron Microscopy Biological Applications. Compiled by F. Scanga. Pp. xxvi + 331. (Amsterdam, London, New York: Elsevier Publishing Company, 1964.) 210s.

INSPIRED by the magnificent X-ray tube with spinning target designed by Muller1 and now in operation at the Davy Faraday Laboratory of the Royal Institution, we have considered the feasibility of completely sealing off the rotating anode by means of mercury after the manner of the classical Torricelli experiment.

MANGROVES have been of interest to botanists ever since the first details were given by morphologists in the eighteenth century, not only to specialists in ecology on account of their somewhat peculiar distribution as shore-line vegetation, but also to the general botanist in view of the unusual morphological and physiological features which they display. It is therefore satisfactory that it has been found possible to give a very full account of the main features of these plants as observed by the 1939 Cambridge Expedition to Jamaica1. Those of us who have attempted field experiments even a short distance from the laboratory will realize full well the difficulty in assessing requirements beforehand, and it can well be understood that the performance of the Expedition falls short of its members' expectations on this account and in view of the scanty data already in the literature on which they had to rely for guidance. Nevertheless, in spite of these unavoidable difficulties and notwithstanding the cessation of activity due to the outbreak of war, Dr. Chapman presents a most impressive series of three articles ranging over a wide field of endeavour. It is stimulating to find here a clear grasp of the problems involved in attempting to relate morphological character to physiological function, with repeated emphasis on the problems yet to be solved. Work of this kind can clearly not be final, and probably the most useful feature of the Expedition, as it is reflected in these papers, lies in the guidance it gives for more detailed investigation which may become possible in the future.

IN the death of Prof. J. H. Priestley the botanical world and the Department of Botany of the University of Leeds have lost a man of originality and genius. Though cut off from fulfilling the period of university service to the usual age of retirement, his life has been a full one, and the record of his achievements is one of which any man might be proud.

FEW studies in biochemistry have aroused such popular interest as the remarkable advances made in recent years concerning the dependence of animals on small doses of those substances, produced mainly by plants, which we call the vitamins. It is natural that the marked heterotrophy for these substances in man has stimulated interest largely in the vitamin aspects of animal nutrition ; but it has always seemed anomalous that the importance of vitamins to the plant which makes them, realized only vaguely even by many botanists, has not had wider publication. This gap has now been filled in this remarkable book, and it is well that the first major review should come from the hands of an expert, and indeed one who may be said to be the founder of the modern science of plant vitaminology. His book is, as it must be, of the nature of a preliminary report on a subject now in the full tide of development ; but it tells, in an orderly way, of all the important advances made in the ten years since Schopfer (1934) first showed the necessity for vitamins in the culture of Phycomyces, with sufficient bibliography to enable enthusiasts to find other sources of information. It is further very satisfactory that the author, though not hesitating to reproduce and discuss the structural formulae of the vitamins and to emphasize the vitally important, if purely chemical, aspects of vitamin structure, does not fall into the trap of making the work biochemical. It is a book written by a plant physiologist for plant physiologists. Plants and Vitamins By W. H. Schopfer. (A New Series of Plant Science Books, Vol. 11.) Pp. xiv + 300. (Waltham, Mass.: Chronica Botanica Company; London: Wm. Dawson and Sons, Ltd., 1943.) 4.75 dollars.

THE celluloso of the cell-wall and fibres of most plants contains closely associated polysaccharide material which is generally a xylan. The cotton hair is unique in being free from xylan, but manilla hemp, jute and sisal, for oxamplo, may contain as much as 15–20 per cent. The view has been put forward tentatively that tho xylan molecules in such fibres participate in the micelles and are oriented in the same direction as the cellulose chains1: the period along the fibre-axis of xylose residues in oriented xylan would be very much tho same as that of the glucose residues in cellulose, and their presence should make no fundamental difference to the X-ray photograph. Tn support of this view there is the well-known fact that actually no such difference is observed in the ordinary way.

The Plant Cell-Wall By Prof. Pieter A. Roelofsen. (Encyclopedia of Plant Anatomy, Band 3, Teil 4.) Pp. vii + 335 + 68 plates. (Berlin-Nikolassee: Gebruder Borntraeger, 1959.) n.p.

Physiology and Biochemistry of Algae Edited by Ralph A. Lewin. Pp. xxvii + 929. (New York: Academic Press, Inc.; London: Academic Press, Inc. (London), Ltd., 1962). 229s.

The Plant Cell Wall A Topical Study of Architecture, Dynamics, Comparative Chemistry and Technology in a Biological System (International Series of Monographs on Pure and Applied Biology Plant Physiology Division.) By S. M. Siegel. Pp. xix + 123. (Oxford, London, New York and Paris: Pergamon Press, 1962.) 42s.

THE so-called ‘crossed fibrillar’ structure observed in the walls of some plant cells1,2,3 and inferred in a variety of others4 still awaits explanation, and although the evidence for its presence in the latter cases can scarcely be considered satisfactory5, this type of structure is sufficiently widespread to present a problem of the first magnitude in cell-wall physics. Several attempts have been made in these columns and elsewhere to define the underlying mechanism, and it is the purpose of this note to point out a new possibility which arises from the recent work of Astbury and Bell6. The importance of the organization of the protoplasmic surface in considerations of wall structure is now slowly being realized, and recent evidence1 suggests that it is in this surface that we are to seek the mechanism involved in the regular alternation of chain orientation implied by the crossed fibrillar structure. Now in the recent emendation put forward by Astbury and Bell of what may be called the ‘classical’ model of protein structure, the fibrous proteins keratin and myosin are considered always to be effectively in the β-configuration whatever the state of folding [see Figs. 1, 2 and 3, p. 698 of this issue for diagrams of the α- and β-configurations; the supercontracted form would resemble the diagram given by Astbury and Bell for the globular proteins]. The contraction of the α- or of the β- form to the supercontracted condition now corresponds in this model to an effective rotation of the constituent protein chains to the transverse direction.

DURING the recent nuclear tests carried out by the United States Atomic Energy Commission, We have checked the radioactive fall-out in Kingston, a small Ontario town situated some 2,200 miles north-east of the testing grounds. Our sampling period extended from February 15 to May 28, 1955, and included all the test explosions reported by the Press.