476 



NATURE 



[April 15, 1922 



Letters to the Editor. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return^ or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications^ 



The Atomic Vibrations in the Molecules of Benzenoid 

 Substances. 



Sir William Bragg has recently suggested 

 (Presidential Address to the Physical Society, Proc. 

 Phys. Soc, 1921, 34, 33) that in the molecule of 

 crystallised naphthalene the carbon atoms are 

 arranged so that in the accompanying figure the 

 centres of atoms at h, I, b, g, e, c lie in a plane, whilst 

 those at k and a lie above the plane and those at / 

 and d an equal distance below it. 



If this were the normal stable arrangement in 

 naphthalene and its simple derivatives, enantio- 

 morphism would result in the case of all mono- 

 substituted, and in the majority of the higher sub- 

 stituted compounds, the special examples of symmetry 

 being obvious on inspection. Since, however, all 

 the available evidence tends to show that the mole- 

 cules of naphthalene derivatives are identical with 

 their mirror images, it follows that the structure 

 suggested by Sir William Bragg represents a phase of 

 an oscillation of the relatively unrestricted molecules 

 of the fused or dissolved substance in which the pairs 

 of carbon atoms k, a and /, d appear alternately 

 above and below the plane containing the six remain- 

 ing atoms. At the first glance such a process appears 

 peculiar and unsymmetrical, but this objection dis- 

 appears when it is noticed that an identical result 

 is obtained if all the atoms are supposed to be in 

 motion in such a way that adjacent atoms move in 

 opposite directions and to an equal distance from 

 the plane of the original ring. If the component 

 perpendicular to the plane of the ring is x, then the 

 condition arrived at is shown below, x and {x) signify- 

 ing, respectively, above and below the plane of the 

 ring. 



By rotating about the axis figured, the second 

 position is obtained with six atoms in the plane of 

 the original ring and four arranged as indicated 

 {y>x and <2x). A similar vibration of the phenan- 

 threne molecule would demand in the case of an 

 isolated phase that the atoms lie in two planes parallel 

 with that of the original ring, and also in four parallel 

 planes containing carbon atoms to the number of 

 two, six, five, and one, respectively. The above 

 argument is circular to the extent that the naph- 

 thalene configuration was partly derived by analogy 

 with the hexagonal rings of the graphite layers, but 



the point is that if independent evidence is forth- 

 coming that an individual naphthalene molecule in a 

 crystal has the arrangement of atoms put forward 

 by Sir William Bragg, then at the same time at 

 least one mode of vibration of the benzenoid molecules 

 will be clearly indicated. R. Robinson. 



Chemistry Department, The University, St. Andrews. 



Transport of Organic Substances in Plants. 



In a letter in Nature of February 23, p. 236, 

 under the above title. Prof. H. H. Dixon and Mr. 

 N. G. Ball put forward the view that the wood of 

 the vascular bundles provides the main path for 

 the removal of the organic materials formed in foliage 

 leaves to places of storage or conversion, the structure, 

 form, and arrangement of the bast (phloem) being 

 regarded as precluding any important longitudinal 

 transmission within it. 



I venture to doubt if the view that the phloem 

 may serve as an important carbohydrate-conducting 

 tissue merits such summary dismissal as the writers 

 of the letter would appear to suggest. 



In the first place, it is somewhat misleading to state 

 that this belief ..." seems to be based entirely 

 on ringing experiments," unless this statement is 

 intended to apply only to the " older writers." In 

 an article on the Translocation of Carbohydrates 

 {Science Progress, October 1910, January 1911) I 

 attempted to bring together the available evidence 

 from anatomical and experimental studies, and a 

 perusal of that paper should show the wider basis for 

 the view put forward by Czapek in 1897 that the 

 phloem is to be regarded as the chief tissue concerned 

 in the conduction of organic material in the plant. 

 In later papers {Annals of Botany, 1915, 1917) I 

 dealt with many of the points which call for considera- 

 tion in any investigation of this problem, and indicated 

 the nature of results obtained by the application of 

 Senft's method of locating sugars by the formation 

 of their osazones. Unfortunately, the war and the 

 heavy pressure of departmental duties have held up 

 the work, and it has not yet been possible to publish 

 results in detail. 



The following comments may be made, however, 

 in connection with the view put forward by Prof. 

 Dixon and his collaborator. The sugars are described 

 as having to traverse the cross-partitions (of phloem 

 cells) as a stream if they use this tissue as a conduit. 

 It may be doubted whether the movement can be 

 compared to the mass movement of water in a tube, 

 and other considerations have been urged in the later 

 paper referred to above. 



Experiments made by Czapek (referred to in my 

 last paper, pp. 293, 294, 303) showed that removal 

 of starch from an attached leaf continued if a short 

 length of the petiole was plasmolysed (but not killed), 

 that a killed (boiled) portion of petiole prevented 

 translocation permanently, but that a narcotised 

 portion only temporarily interrupted the process, 

 which was renewed on recovery of the tissues. 

 Though perhaps not altogether excluding the possi- 

 bility of conduction in the wood, such experiments 

 appear to point to the activity of living cells in the 

 transportation, and I have suggested a possible 

 explanation of the continuance of the process in 

 plasmolysed (living) cells, assuming the sieve-tubes 

 to be the channels concerned {loc. cit., p. 303). 



Various histological features of sieve-tubes and 

 their associated cells appear to harmonise well with 

 the view that they serve to conduct carbohydrates, 

 e.g. their continuity, distribution, and degree of 

 development in different types of plants, the structure 

 of the sieve-plate, the distribution of connecting- 



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