118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE. BY C. R. NODDER, M.A. (THE LINEN INDUSTRY RESEARCH ASSOCI-4TION) Received May I 6th, I g 2 4.The structural and optical characters of the flax fibre, and of so-called bast fibres in general, have attracted the attention of numerous investigators from the time of Nageli’s pioneer work ( I 862) down to the present day. The present state of our knowledge in this field has recently been thoroughly reviewed by Keimers,l who gives a very useful list of references to the literature. Zsigmondy, in his (‘ Kolloidchemie,” and Freundlich, in his ‘( Capillarchemie,” 3 refer in some detail to cellulose fibres as examples of colloid gels. The bast fibres, of which flax may be taken as typical, are very noteworthy examples of structures which combine crystalline and colloid properties. I t is the purpose of this paper to review briefly the more important considerations which have led to the recognition of this double r81e and, further, to discuss in some detail a number of observations of characters of the flax fibre-mainly structural-which are of interest on account of their possible physico-chemical relationships.Such a review seems very desirable at the present time, since references to the subject in English literature are very scanty; much of the work has appeared in continental publications which are not readily accessible, for example, the paper by Reimers referred to above. Little need be said regarding the general colloid properties of cellulose fibres, as these are now well recognised. These properties are manifested in the sorptive power of the fibres, their swelling behaviour in water and in various aqueous solutions and in the undoubted colloid properties of solutions of cellulose and its derivatives.The point of fundamental importance is the recognition of the cellulose fibre as a two-phase system in which the cellulose particles collectively present a very large surface. An insight into the form and arrangement of the cellulose particles may be obtained by microscopic examination of fibres which have been suitably treated. Thus when a flax or ramie fibre is mounted in water or other suitable medium and vigorously compressed beneath the coverslip (e.g. with the tip of a scapel) innumerable fissures become evident and the fibre-wall 1 H. Reimers, ‘‘ Die, Verschiedenheiten im strukturellen Aufbau der Bastfasern. 23rd edition, 1920. See also ‘‘ Report of Discussions on Colloids,” Trans.Faraday 32nd edition, 1922. Mitt. Deut. Forschungs-Instituts f. Textilstoffe in Karlsruhe,” 1920-21, pp. 109-282. SOL, 1921, PSI. 251252 SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE becomes divided into extremely fine fibrils, spirally arranged.’ It is often possible by compressing the fibre to a sufficient extent to bring about such a subdivision of the fabrils that they pass beyond the limits of microscopic visibility. There can be little doubt of the close relationship between these visible fibrils and the colloid particles of the cellulose gel. The optical be- haviour of the fibrils and of the fibre-walls as a whole show them, as we shall see, to be essentially crystalline. Nageli’s conception of the structure of vegetable membranes was remarkably near the truth ; he recognised, indeed, the crystalline character of the sub-microscopic particles, to which he gave the name micelles.” Stmcture.-The structure of the fibre will now be considered in some detail as a necessary preliminary to a description of its optical behaviour.The fibre is not homogeneous, but shows several layers which differ in their properties. In cross-sections of typical flax fibre-bundles the true middle- lamella is seen between the fibres as a very delicate membrane, somewhat thickened at the corners, which stains deeply with ruthenium red and appears uniformly dark between crossed nicols. Within the middle-lamella, and forming the outermost layer of the fibre itself, is the thin “primary layer ’’ which is distinguishable according to Reimers-who agrees with Dippel and other earlier workers-by the fact that it appears bright when thin cross-sections are examined between crossed nicols ; it is stated that, on account of a Brewster-cross effect, actually only those parts of the fibre- sections which are in the diagonal setting appear bright.In the case of flax this primary layer is very thin and not readily discernible, but a thin outer layer of the fibre, diKering in properties from the inner layers, may be distinguighed in another way which I. believe has not been previously described. Within the primary layer are the ‘‘ secondary layers ’’ which in strictly transverse sections do not transmit much light between crossed nicols. Although a definite Brewster-cross effect is not readily seen in transverse sections of the flax fibre, it is probable that in common with bast fibres in which a Brewster cross is observedY3 flax has the radial structure to which this effect is due.This is a matter, however, which calls for further careful investigation. Reimers describes hemp as showing imperfect crosses. Nageli and Schwendener (1877) described the production of the Brewster cross by sections of the tracheids of Pinus. I t may not be generally known that flax fibres transmit light very readily in the longitudinal direction, so that the fibres appear bright in cross-sections of the stem as much as half-an-inch in thickness. This is especially striking after the section has been treated with caustic soda solution, when the fibres appear bright yellow.Care- ful observation of thick sections stained with ruthenium red illuminated by both reflected and transmitted light shows that a thin outer layer of the fibre wall, adjoining the rniddle-lamella, does not transmit light in a longi- tudinal direction nearly so readily as the interior layers, so that it appears opaque in sections of +-inch or less in thickness. This difference is pre- sumably to be referred to a difference in the orientation of the micelles in This is referred to below. 1 X rough idea of the fineness of the fibrils is given by the illustration of a compressed ramie fibre in 7. Text Inst., 1922, 170, Fig. 16. For making evident fibrils of the greatest possible fineness a strong solution of calcium chloride tinted with iodine seems most suitable as the mounting medium in which the fibre is compressed.”ee Reimers, loc. cit., p. 119, Dippel, L., 1869, ‘L Das Mikroskop u. seine Anwen- dung” (Braunschweig), 2 Teil, pp. 129, 310, 322. .i E.K. willow, see Reimers, Loc. cif., p. 209.SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE 253 the outer layer, a suggestion which appears to be in agreement with differences which have been recorded in the form and orientation of the optical indicatrix in the primary and secondary layers of various fibres.l The (‘ beading ” effect often observable when flax fibres are swollen by the viscose method,2 is apparently due to the lesser power of swelling possessed b y the “ primary layer ” of the cell-wall and the irregular folds which were described as sometimes visible in the wall of compressed flax fibres are probably in this layer.The number of secondary layers which may be clearly distinguished in cross-sections of flax fibres which have not been specially treated is rarely more than ten and is usually less.* I n fibres viewed longitudinally, Q number of layers may often be distinguished in optical section and give to the fibre a longitudinally striated appearance. Fibres compressed beneath the coverslip as described above show these layers more distinctly, but it has only been possible to distinguish clearly some twelve or fifteen layers in fibres thus treated. Searle,5 however, has recently shown that in cross-sections swollen with 15 per cent. caustic soda solution and compressed beneath the coverslip it is possible to distinguish quite a large number of layers (about 50).The picture which one has formed, therefore, of the flax fibre is that it is built up of numerous layers, each with a spiro-fibrillar structure. Before the optical properties of the fibre are described it will be advis- able to consider more fully the nature of the spiral arrangement of the fibrils. Flax fibres which have not been subjected to a special compression treatment often show fine, more or less longitudinal, fissures in the cell- wall.6 I t is easy to show, by compressing the fibre beneath the cover-slip, that these fissures follow the trend of the fibrils. Observation of the slope of the fissures in the untreated fibres leads to the conclusion that the fibrils run, on an average, at an angle of about IO’, or rather more, to the axis of the fibre.In fibres which have been moderately compressed beneath the cover-slip it may readily be seen that the fibrils in the outer secondary layers run in left-handed spirals-the spirals of an ordinary wood-screw being considered as right-handed. The fibrils of the inner layers have been described as sometimes running in right-handed spirals. I t is not unlikely that observers have been deceived in this connection by an optical effect (Welcker’s effect). If the microscope is slowly racked down when an object possessing very fine fissures is under observation it is seen that the first image of a fissure is a dark line-it being assumed that the object is mounted in a medium of lower refractive index. When the microscope is focussed a little lower the image of the same fissure is a bright line.When a flax fibre with walls of a suitable thickness is under examination the appearance of internal spirals with opposite twist may be produced as follows : as the microscope is racked down the dark images of the fissures on the upper half of the fibre are first seen ; at a slightly lower focus the dark images of the fissures on the lower half of the fibre come into view ; then follow the bright images of fissures on the upper and lower half of the fibre respectively. Since the possibility of deception by Welcker’s effect 1 E g . Reimers, Zoc. cit., p. 193. 3r. Text. Inst., 1922, p. 164, Fig. 5. 4 We may note here that the secondary layers show differences in that they stain increasingly more deeply with ruthenium red as the lumen is approached ; the outer layers show very little affinity for this stain.Linen Industry Reseach Association, Memoir No. 20 (1924). 1.e. in the secondary layers which form the bulk of the fibre-wall. the primary wall of flax fibres has not been satisfactorily determined. See, for example, Searle, Zoc. cit. The structure of VOL. XX-T9254 SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE has been realised a considerable number of flax fibres have been examined but in no case was the presence of right-handed internal spirals discernible, even in the broad fibres from the base of the stem. If they really occur, the cell-wall layers with a right-handed spiral structure are probably always relatively thin, and possibly of rare occurrence ; certainly the characteristic- anti-clockwise drying twist of flax seems never to be disturbed.Double Refractz’on.-Flax fibres are strongly double refracting, sur- passing in this respect the micas among minerals, so that interference colours up to a green of the second order are observed between crossed nicols. In longitudinal view the fibre as a whole shows straight extinc- tion ; but this behaviour appears to be due to the combined action of the upper and lower halves of the fibre as it lies on the stage of the microscope, i.e. due to a compensating action of the fibrils in the upper and lower halves, since they lie inclined in opposite directions with respect to the axis of the fibre. Thus, if a fibre is compressed in the manner described above it is possible to separate the fibrils to such an extent that in places they are not crossed by fibrils running in a different direction.The fibrils, or groups of fibrils, are then themselves seen to show straight extinction between crossed nicols. The observations of Balls (Zoc. lit.,. p. 77) appear to show that in the cotton hair the extinction of the fibrils IS oblique, When flax fibres are swollen with caustic soda solution and compressed it is found that the separate fibrils or groups (bands) of fibrils still show double refraction (first order grey) and straight extincti0n.l The existence of double-refraction in the fibrils themselves, even when swollen, seems fairly good evidence that the double refraction of the fibre is not due to internal tensions.Further and more convincing evidence is given by Searle (hc. cit.) who shows that the minute fragments produced by the breakdown of tendered flax fibres are doubly refracting. The optical behaviour of the fibre is thus seen to suggest very strongly that we are dealing with a crystal, or more correctly, a crystalline aggregate, since thin transverse sections of the bast-fibres in general give rise to a Brewster-cross effect. It is not difficult to determine the optical sign of the fibre-walls and the character of the indicatrix. Measurements of the refractive indices have been made by various observers. Herzog2 gives figures obtained by an immersion method. The mean refractive index is about 1.56 at zoo C. for sodium light and lies therefore between that of Canada balsam and that of aniline.On account of the double refraction of the fibre no liquid medium can be found in which its outlines are invisible in unpolarised light.3 Herzog’s results show that the specific birefringence is as high as 0.067.~ The use of a selenite plate shows that additive colours are obtained when the principal axis of the plate is parallel to the length of the fibre- or, where isolated portions of the cell-wall are being examined, parallel to the fibrils-and, sitice the small amount of light transmitted by cross- 1See Fig. 14, 7. Text Ivtst., 1922, p. 169. J Herzog, A., g b Llchtbrechung u. Mikrophotographie von Faserstoffen, Mitt. Fors- chungs-Instituts, Sorau,” 1920~21. 4 See also Remec, B., ‘‘ U ber die spezifische Doppelbrechung der Pflanzenfasern.Sitzungsberichte der Kais. Akadamie der Wissensch. in Wien, Mathem. naturw. Klasse,” 1901. Bd. 60, Abt. I, 364-87 ; Korn, R., b b Unterscheidung einiger Fasern, insbes- ondere der Leinen- u. Hanf-hser, Jahresb. d. Verein f. angew. bot.,” 1909, Bd. 7, 189 ; Dissertation Berlin, 1916, and Ambronn, Herm., ‘‘ Ueber eine neue Methode z. Best- immung der Brechungs-exponenten anisotropischer mikroskopischer Objekte. Ber. d, mathem. physik. Klasse d., Kgl. Sachs. Ges. d. Wissensch. zu Leipzig,” 1893. Herzog, A., ‘‘ Textile Forschung,” 1922, No. 2, p. 58.SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE 255 sections of the fibre between crossed nicols indicates that there is no great difference between the refractive indices a and fl, it is concluded that the fibrils or crystallites composing the fibre-walls are optically positive, i.e., light travels with the lowest velocity in the fibre when its vibrations are parallel to the fibrils. The use of a selenite plate in connection with cross-sections of the fibre shows that the shortest axis of the indicatrix is radial.The longest axis is parallel to the fibrils and the inteimediate axis lies tangen- tially and at right angles to the fibrils. These relationships of the indicatrix, which are generally true for the secondary layers of bast fibres, were first made clear by Dippel (Zoc. cit., 1 8 6 9 , ~ ~ . 318). Nageli and Schwendenerl obtained similar results from an exaniination of the tracheids of Pinus. It has been shown in the case of ramie that when the fibres are nitrated the optical sign becomes negative.When the cellulose is regenerated, by the use of ammonium sulphide, the fibres become again positive. This behaviour would seem to offer a further argument against the view that the double refraction of the fibre may be due to internal strains. The nitrated fibre may be regarded as a pseudomorph after cellulose. PZeochroism.-Flax fibres when stained with methylene blue, congo red, safranine and many other dyes show very pronounced pleochroi~m,~ with strong absorption of light when the axis of the fibre is parallel to the vibra- tion plane of the polariser. Fibres stained with iodine show a pleochroism almost as pronounced as that of biotite as seen in rock-sections. This behaviour lends some support to the view that the fibre is a crystalline aggregate; it is probably due to the oriented arrangement of the coloured particles, although according to Zsigmondy the arrangement of the particles at different distances apart in different directions is an alternative explana- tion of such an effect. Ambronn has shown that all the substances examined which confer pleochroism on the fibre are themselves pleochroic.* Of interest in this connection are the results obtained by Gaubert who shows, for example, that phthalic acid crystals coloured with methylene blue are pleochroic.X-ray S)kctrog7aphic Experimnts.-Further evidence of the crystalline nature of the cellulose in the flax fibre is obtained by the application of the method of Debye and Scherrer.g Herzog and Jancke have obtained point-diagrams with flax and ramie fibres in parallel arrangement which they consider show clearly their crystalline structure, with a rhombic (or possibly monoclinic) symmetry for the component crystallites. With powdered fibres Debye-Scherrer rings are obtained, the character of which points to similar conclusions.Herzog and Londberg have recently shown that when cellulose fibres are nitrated and then denitrated the regenerated cellulose has the same X-ray spectrographic characters as the original fibres, i.e., the chemical reactions have not disturbed the orientation of the cellu- lose particles. The conception of the flax fibre as a concentrically lamellated spiro- fibrillar crystalline aggregate with colloidal properties is closely similar to 1 Nageli, C., and Schwendener, S., “ Das Mikroskop,” 2nd edition, 1877, Leipzig.2 Hans Ambronn, Koll. Zeitschr., 1916, IS, 80, 273. 3 Ambronn, Herm., I‘ Pleochroismus, Ber. d. D. Bot. Ges.,” 1888; A m . Phy~., 1888,3+ 341 ; 1889,38, 160. 4 Zslgmondy makes frequent references to Ambronn’s work in his Kolloidckemie, 3rd edition. Gaubert, P., I@-10, e.g., C.r., 1909, 149, 10004-106. Phys. ZEit., 19x7, 18, 291. 7 Ber. d. D. Cli. Gss., 1920, 53, 2162. Be*., 1924, 57, p. 329.256 SOME STKUCTURA4L CHARACTERS OF THE FLAX FIBRE Balls’ conception of the cotton hair. With such a conception in mind we may now pass on to consider some further characters of the fibre. Dislocation Marks (Verschiebungen).-Now that the essentially crystal- line nature of the fibre is, as I. believe, fully established there seems to be little difficulty in accepting the view that these transverse markings of the fibre are due to a twinning similar to that produced in minerals by pressure (e.g., calcite, carnallite, mica). When the fibre is in a position of extinction between crossed nicols the dislocation marks appear bright.The be- haviour of a fibre when it is rotated between crossed nicols suggests that the dislocation marks have themselves straight extinction, although they rarely appear quite dark. The transverse markings often give rise to a cross-like appearance in the fibre. In such cases careful focussing shows we are dealing with a dislocation in the upper side of the fibre overlying a dislocation in the lower part of the fibre. The markings are in fact always approximately at right-angles to the trend of the fibrils.In consequence of this, hemp fibres, in which the fibrils run in right-handed spirals, may be distinguished from flax by a careful examination of the dislocation marks. Searle has recently shown that the transverse marking are of considerable practical importance in that they are points of weakness in the fibre. Ex- cessive mechanical treatment of flax (e.g., in scutching) is found to produce large numbers of dislocation marks and the fibre is at the same time weakened. The cause of this weakness is probably the minute fissuring, or local lateral separation of the fibrils, in the neighbourhood of a dislocation mark. This fissuring is, moreover, probably the cause of the more intense staining of the dislocation marks that is obtained with iodine solution and other reagent^,^ and as Searle points out here also the fibre is most susceptible of attack by hydrolytic and oxidising agents.I t has been pointed out that the transverse markings of the cotton hair also are often accompanied by fissures which give rise to the appearance of rows of pores (de Mosenthal’s ‘‘ Stomata ”). There is clearly a close resemblance between the transverse markings of the cotton hair and those of the flax fibre. Balls7 and Denham * have recorded similar conclusions regarding the nature of the transverse markings of the cotton hair and (Denham) of de Mosenthal’s (‘ Stomata.” Transverse markings are often extremely numerous in fibres taken from a bleached fabric. Careful observation usually reveals the presence of numerous fine markings which at first pass unnoticed. Pre- sumably all these markings are due to mechanical forces imposed on the fibres during the various processes which the fabric undergoes.Searle shows that fibres tendered by over-bleaching develop ‘‘ planes of segmentation ” See also Ambronn, Ztschr. f. wissensch. Mikroskokie, 1918, 32, 9, 32, or Zsig- Reimers, H., Textilberichte, 1921, p. 381 ; Herzog, A., Mitt. Forschungs. Institiits. mondy, Kolloidchernie, 3rd Edn., 1920, p. 112. Sorau, 1920-21, p. 41 ; Nodder, C. R., y. Text. Inst., 1922, 215. 3 Linen Industry Research Assn., Memoir No. 20, rgnq. Miiller, W., Faserforschung, 1921, Vol. I., No. I, p. I (‘‘ EinAuss und Erkennung mechanischer Behandlung der Flacnsfaser ”).Herzog, A., Mitt. Forschzrngs. Instituts. Sorau, 1920-21, p. 40 (*‘ Ueber die Ursachen des Stumpfwerdens der Flachsfaser bei der Kiinstlichen Trocknung des Rostflachses ”) ; Nodder, C. R., J. Text. Itrst., 1922, No 10, p. 215. I believe Herzog was the first to point out the true nature of de Mosenthal’s 64 Stomata ”-Herzog, A., Knnststofe, I, 1911,425 (‘* Uber das mikroskopische Verhalten der Baumwolle in Kupferoxydammoniak ”). When my observations were published (y. Text. Inst., 1922, p. 213)~ I was not aware of the existence of Herzog’s paper. 7 Balls, L., Proc. Roy. SOC., 1923-24, Series B, 95, p. 72. a3!. Text. Inst., 1923, 14, T . 85.SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE 257 at the transverse marks when swollen with caustic soda solution and gently pressed beneath the cover-slip ; at the same time the fibre-wall breaks down in a direction parallel to the trend of the fibrils, so that numerous short rod-like fragments are produced.He shows, further, that fibres tendered by different agencies show considerable variation in behaviour when sub- mitted to a similar treatment. Thus fibres tendered by the action of micro-organisms do not show the numerous ‘L planes of segmentation ” characteristic of over-bleached fibres. If it is conceded that the transverse markings are especially liable to chemical attack their presence in the fibre is of interest with reference to the surprising differences in the viscosities of solutions of cellulose which are brought about by such apparently gentle treatments of the fibre as a boil in weak sodium carbonate solution.I t is conceivable that extremely numerous sub-microscopic dislocations are present in the fibre and form preferential points of attack of chemical reagents, and that when the cellu- lose is dissolved the fibrils break transversely at the attacked points. The shorter length of the fibrils in a solution obtained from more heavily at- tacked fibres would afford a possible explanation of its lower viscosity. Twisting Behaviuur.-As we have seen, flax and hemp fibres differ in that the fibrils composing the secondary layers run in left- and right-handed spirals respectively. The fact that the drying twist of the fibres is in op- posite directions is closely related to this structural difference.’ The twist- ing behaviour appears to be explicable on the assumption that there is a differential contraction or elongation of the fibrils in different layers of the cell-wall.When a fibre is treated with caustic soda solution, say of 40° Tw., there is a considerable contraction in length and a twisting movement in the direction which one would twist the fibre if an attempt were made to untwist the fibrils (as one would untwist the fibres in a yarn). If a short piece of a fibre (say I mm. long) is treated with caustic soda solution the appearance produced suggests that the outer layers contract more than the inner layers since the cut ends become convex.2 I t seems probable, therefore, that the ‘‘ untwisting ” behaviour on mercerising, or wetting (which also produces a small contraction in fibre length), is due to the greater contraction of the fibrils in the outer secondary layers of the cell-wall,3 the fibre acting as a multiple Breguet spiral with very high pitch.Since on wetting with water the contraction in fibre-length is very small (possibly niZ if the fibre is under a small tension) whereas the untwisting is very vigorous, it would appear that in this case the contraction is practically confined to the outer layers. SweZZing-It is not proposed to deal with the swelling properties of the fibre in detail on this occasion. We may note, however, that fibres are in general found to swell to the greatest extent in the direction of the shortest axis of the optical indicatrix, i.e., radially. If an ellipsoid is constructed to represent the swelling properties of the fibre it is found to bear a re- ciprocal relationship to the optical indi~atrix.~ In a general way this be- 1 If a wet flax fibre is held at one end and allowed to dry, the free end (held towards one) is seen to move in a clockwise direction.The difference in twisting behaviour of flax and hemp was apparently first described by Sonntag (Ber. d. D. Bot. Ges., 1911, 3, 2 Cf. Fig. 15 ; y. Text. Imt., 1922, p. 216. 3 The primary layer, of flax especially, is considered too thin to have an appreciable 4 Schwendener, S., ‘‘ Ueber Quellung u. Doppelbrechung vegetabilischer Membranen. 669). influence in this respect. Sitzungsb. d. Kgl. Akad. der Wissensch. zu Berlin,” 1887, 659-702.258 SOME STRUCTURAL CHARACTERS OF THE FLAX FIBRE haviour may be explicable as the result of the forcing apart of the ultimate fibrils or micelles of the fibre by the absorbed liquid.The contraction of the fibre in length in caustic soda solutions may in part be similarly explicable, as may be seen from the behaviour of wire-models made to illustrate the spiro- fibrillar structure of the fibre. In connection with the action of caustic soda solutions on bast fibres one or two points of interest may be noted. I t has been shown that 10 per cent. solutions produce a remarkably well- defined maximum contraction in single flax and ramie fibres (under a very small tension). There appears to be no sharp change in any physical property of caustic solutions at this strength ; the effect is probably closely related to changes in the degree of hydration of the sodium ion. There is, further, a pronounced flattening of the concentration-contraction curve with solutions containing about 15 per cent. of caustic soda, i.e., solutions with maximum specific conductivity for electricity. It is of interest to note that Collins and Williams in a recent paper record a maximum swelling of cotton hairs with solutions of caustic soda and caustic potash of maximum specific electrical conductivity. An outstanding question of great interest is the cause of the spiral ar- rangement of the fibrils and of the opposite direction of the twist in differ- ent fibres. I t is not yet clear whether the protoplast has the determining influence in this respect or whether the stereochemical properties of the cellulose play a part. Since the structure of the fibres is clearly related to the mechanical needs of the plant it might be argued that the pitch and direction of the spirals is determined by the activities of the protoplast, but such a (teleological) argument will not find favour with the majority of biologists nowadays. In hemp fibres the slope of the fibrils with respect to the long axis of the fibre is very small-about go-and this appears to supply an argument in favour of the view that the protoplast has the determining action; such a slope seems too small to be accounted for by a definite stereochemical property of the cellulose. Nodder, C. R., and Kinkead, R. W., y. Text. Iust., 1923, p. T 133. ". Text. Inst., 1924, T 154.