December 23, 1922] 



NA TURE 



'0/ 



and chlorophyll b was estimated from data obtained, 

 due allowance being made for the energy diffusely 

 reflected by the leaf. The results were of the follow- 

 ing order : for the yellow-red (570-640/^), 15 calories 

 per c.c. of carbon dioxide, for the green (510-560^^), 7, 

 and for the blue (430-510/^), 22 +, these being 

 maximal values. 



Mr. Briggs pointed out that since the heat of 

 formation of the most probable products of assimila- 

 tion ranges from five to six and more calories per c.c. 

 of carbon dioxide, the indications are that both 

 chlorophyll a and chlorophyll b take part in the 

 photochemical reaction. Referring to Prof. Baly's 

 suggestions as to the part played by the different 

 pigments in the photosvnthetic process, he said that 

 since the quantity of each pigment underwent 

 relatively little change during prolonged assimilation 

 no energy was supplied from this source, and, further, 

 that since as much oxygen was evolved as carbon 

 dioxide absorbed in the red and the green parts 

 of the spectrum — regions where no energy is absorbed 

 by the xanthophyll — as well as in the blue, it was 

 not necessary to postulate a photochemical reaction 

 involving xanthophyll in order that oxygen might 

 be liberated. 



Prof. I. M. Heilbron and Mr. C. Hollins put forward 

 some speculations on photosynthesis. The large 

 number of plant products in which the predominant 

 carbon nucleus is C 5 or a multiple of this suggests 

 that this unit has a special significance. The photo- 

 synthesised reactive hexose may be supposed, in 

 addition to its further condensation to sugars, 

 cellulose, glucosides, etc., to furnish by dehydration 

 u-hydroxymethylfurfural. This by oxidation and 

 decarboxylation can give a stabilised C 5 compound, 

 which, either as the furan derivative or (by opening 



of the ring) as dihydroxyglutaconic dialdehyde, may 

 be a source of pentoses and of condensation products 

 of these. Simple schemes were suggested showing 

 how two, or three, molecules of a " pentose " can 

 give rise by ordinary condensation reactions to 

 anthocyans (C 15 ), terpenes (C 5 , C 10 , C 15 , etc.), coniferyl 

 alcohol (C 9 ), and the numerous related compounds, 

 coniine (C 8 ) and the phonopyrrolecarboxylic acids 

 (C 8 , etc.). The degradation of hexose into " pentose " 

 represents the respiration of the plant. Against the 

 suggestion of Robinson (British Assoc, 1921) that 

 anthocyans result from the condensation of two 

 hexose and one triose molecule are to be set the 

 absence of nonoses in Nature and the failure of all 

 attempts to obtain benzene derivatives from hexoses. 



Papers were also contributed bv Dr. F. C. Eve 

 and Prof. M. C. Potter. 



Prof. R. Robinson thought that the accumulation 

 of active formaldehyde and formhydroxamic acid 

 scarcely accounted for the almost inexhaustible 

 variety of plant products. The alkaloids were 

 probably produced from hexoses rather than built 

 up atom by atom from formaldehyde. He was 

 unable to accept the suggestions of Prof. Heilbron 

 and Mr. Hollins as to the significance of the C 5 unit. 

 The anthocyans he preferred to consider as C + C 3 + C 6 

 rather than C 5 +C 5 +C 5 . Although nonoses had not 

 been found in Nature, E. Fischer had obtained a 

 nonose which was fermentable. 



Dr. E. F. Armstrong emphasised the importance 

 of cane-sugar in the carbohydrate metabolism of 

 green leaves. 



Prof. Baly briefly replied to some of the points 

 which had been raised, and the discussion was then 

 closed by a few remarks from the chairman, Prof. 

 Dixon. 



Progress in Engineering. 



T'HE James Forrest lecture delivered in 1903 by 

 -*■ Dr. W. H. Maw dealt with some unsolved 

 problems of engineering ; his presidential address, 

 read before the Institution of Civil Engineers on 

 November 7, directs attention to the progress which 

 has been made towards the solution of certain of 

 these problems. In ordinary researches the con- 

 clusions arrived at often remain untested for more 

 or less long periods, and when they are tested it is 

 not unusual for such tests to develop facts which, 

 if known earlier, would have decidedly affected the 

 character of the research carried out. During the 

 war, especially in aeronautical researches, immediate 

 results were wanted, and reasonable suggestions 

 arising from research were, as a rule, tested without 

 delay. As a result conclusions were arrived at and 

 advances made much more promptly than would 

 have been possible under other conditions. 



For many years past there has been steady growth 

 in the demands for larger structures and machines. 

 In the case of bridges there are three ways in which 

 increases of span may be made commercially attain- 

 able : First, by improvements in the structural 

 designs ; second, by the reduction of the so-called 

 factors of safety now adopted ; third, by the use of 

 improved structural materials and constructive 

 details. Dr. Maw does not think that there is much 

 chance of obtaining material aid by the first of these 

 methods ; it does not appear likely that any new type 

 of design will be evolved possessing striking advantages 

 as compared with those already known and investi- 

 gated. The prospects from the second method are 

 better ; there are two classes of allowances, namely, 

 (a) stresses due to wind pressures, changes of tempera- 

 ture, and so on, which depend upon local circumstances 



! and other matters of individual judgment, so that a 

 reduction cannot be calculated upon, and (6) allow- 

 ances which depend upon the quality of all the 

 materials used and the soundness of the workmanship. 

 The allowances under the latter head might be 

 materially reduced as compared with those con- 

 sidered necessary even ten years ago. During that 

 period, vast improvements have been made in our 

 steel manufacturing processes, especially in the 

 direction of ensuring uniformity of quality, while 

 the facilities for thorough testing and inspection 

 have been enormously increased. 



In reference to the third way, there are no indica- 

 tions that we have reached the limits of progress 

 in the use of improved structural materials. In 

 long span bridges, the importance of the " specific 

 tenacity " of the material {i.e. the ultimate strength 

 in tons per sq. inch divided by the weight in pounds 

 of one cubic inch) is exceedingly great, since the 

 weight of the structure itself forms the larger portion 

 of the total load supported. The successful manu- 

 facture, on a commercial scale, during recent years, 

 of various high-quality alloy steels has quite changed 

 the aspect of affairs and has materially enlarged 

 the limits of the practically permissible spans of 

 different types of bridges. At present, the most 

 hopeful line of progress appears to lie in still further 

 improvements in alloy steels and their treatment. 

 Research work bearing on this subject is being 

 vigorously prosecuted by our leading steel makers 

 and affords every ground for expecting substantial 

 advances. 



Improvements in metallic alloys have been rendered 

 possible by the revelations of microscopical research. 

 Prior to the development of this type of analysis. 



NO. 2773, VOL. I io] 



