AGRICULTURAL CHEMISTRY AND VEGETABLEPHYSIOLOGY.THE investigations in the past year have in the main followed thelines of previous years : there are, however, signs of more move-ment. In France, the Annales de la Science Agronomique has beenrestarted, under the able editorship of M. Albert Bruno, and alreadythere is an increase in the output of scientific work. In Englandand in America, investigations begun after the Armistice are reach-ing the. stage of publication, and certain directions of specialisationcan now be observed. These will be indicated under the variousheadings.Soil Investigations.British soil investigators are studying the biological factors ;American workers are ascertaining the properties and relationshipsof the soil solution and of the soil acidity; whilst Continentalworkers are studying the physico-chemical relationships of the soil.This course is economical of time and effort, but it would be attendedby grave disadvantages if the specialisation proceeded so far as toobscure the fact that all three aspects of the subject are of vitalimportance to the study of soil fertility.The Soil Solution.The soil retains by absorption and surface attractions some10 to 20 per cent. of its weight of water, distributed as films overits particles.The water dissolves some of the soil constituents,forming a solution which is of obvious importance as the mediumthrough which plants and micro-organisms derive their food ; indeedi t may be regarded as the culture solution for the plant.Experi-mental work, however, is hampered by the difficulty of separatingit from the soil ; when soil contains moisture in percentages suitablefor plant growth, the solution is held by the soil particles with suchforce that no ordinary means will remove it.Various methods have been suggested for isolating the solutionfrom the soil. Reasons are advanced for supposing1 that theF. W. Parker, Soil Sci., 1921, 12, 209 ; A,, i, 914.19solution obtained by Ischerekov's displacement method gives amore faithful representation of the soil solution than the othermethods which have been used; ethyl alcohol was the best of thedisplacing fluids tested, and was without observed influence on thecomposition of the soil solution ; successive portions of the displacedsolution gave the same freezing-point depression and contained thesame amount of total solids, whilst the concentration was inverselyproportional to the moisture of the soil.It is, however, difficult to extract the solution, and methods havebeen devised for studying it in situ.It is suggested 3 that a studyof the vapour pressure of the soil would give much valuable informa-tion, whilst the depression of the freezing point has been muchstudied by Bouyoucos in America.show that the latter method leads to substantially the same con-clusions as the 1 : 5-water extraction method used in the UnitedStates.5The water extract has not quite the same composition as the s6ilsolution, but is not greatly dissimilar. When concentrated to havcthe sa'me freezing point, it presumably resembles the actual solutionalso in concentration and should then undergo no change whenplaced in contact with soil.Experiment showed that this was thecase, and probably for the first time in history a solution was pouredthrough the soil and came out unchanged in composition.The relationship between the concentration of the soil solutionand plant growth has previously been studied in the case of barley; 6similar resultls have now been obtained with maize, horse beans,potatoes, and t ~ r n i p s . ~ The concentration a t any point in the soilis not significantly reduced until the plant root actually reaches it,that is, there is no drift of solutes in the soil apart from the move-ment due to drainage.Apparently, however, the fact that a substance occurs in the soilextract affords no certain proof that i t can be absorbed by plants.Orthoclase yields up potassium to water, but the dissolved potassiumwas not absorbable by wheat.It became available, however, whenthe solutions were treated with a mixture of hydrochloric and nitricacids.8 Apparently the solute complex is not dissociated, and theplant is unable to take up the undissociated material.Moagland and his colleaguesZhur. Opuitn. Ap-on., 1907, 8, 147.M. D. Thomas, Soil Sci., 1921, 11, 409.4 D. R. Hosgland, J. C. Martin, and G. R. Stewart, J . Agric. Res., 1920.20, 381; A., i, 214.G. R. Stewart, ibid., 1918, 12, 311.Ann. Reports, 1918, 15, 173; 1919, 16, 172.G. R. Stewart and J.C. Martin, J . Agric. Res., 1931, 20, 663.J. F. Breozeale and L. J. Briggs, ibid., 615; A., i, 388.REP.-VOL. XVIII. 194 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.The variation in composition of soil solution brought about byplant growth affects the degree of dispersion of the colloidal materialof the soil; a large increase in dispersion was observed when thesoil solution was depleted as the result of absorption of solutes bythe plant.9The same change has been studied in a different manner inGermany, where Wiegner's method has been successfully used byvon Seelhorst to study the changes in physical condition of soilbrought about by cropping and manuring.10There is a constant interchange between the colloids of the soiland the soil solution, and the ions affect the state of coagulation ofthe colloids.llSoil Constituents.The soil constituents fall into two great groups-organic substanceswhich have been synthesised in the growing plant and then returnedto the soil either directly or through the bodies of animals or micro-organisms, and inorganic substances derived from the minerals inthe soil, which very often have also passed into plants and.beenliberated on the decay of the leaves, stems, or roots. Among theorganic constituents, one of the most interesting is humus, a black,sticky substance to which important properties have been attributed,although it must be admitted that the direct evidence is not verystrong. Two views have been put forward as to its origin.Beckley l2 supposes that the carbohydrates decompose to formhydroxymethylfurfuraldehyde, which then condenses to formhumus; some experimental evidence is given for this view, whichhas also been put forward inde~endent1y.l~ Eller and K o c ~ , ~ ~ onthe other hand, suppose that humus is formed by oxidation ofquinones which arise by the elimination of water from hexoses.They assign to it the formula C,H,O, :0O- 0Q D. R.Hoagland and J. C. Martin, J . Agric. Res., 1920, 20, 397; A . ,10 C. von Seelhorst, W. Geilmann, and H. Hubenthal, J. Landw., 1921,11 L. Casale, Staz. aperim. apar. ital., 1921, 54, 65.12 V. A. Beckley, J . Agric. Sci., 1921, 11, 69; A., i, 227.l3 J. Marcusson, Ber., 1921, 54, [B], 542; A., i, 313.Ibid., 1920, 53, [BJ, 1469; A., 1920, i, 733.See also W. Eller, Brennetog-Chem., 1921,2, 129; A,, i, 506; H. Stoltzenberg and M. Stoltxenberg-Bergius,2. physiol. C'hem.: 1920, 111, 1 ; d., i, 32.i, 215.69, 5 ; W. Gefimann and A. von Hauten, ibid., 105AGRICULTURAL CHEMISTRY AND VEGETABLE PEESIOLOGY. 195Against this view it is urged 15 that natural humus, unlike benzenederivatives, cannot be sulphonated or nitrated, whilst other ex-periments indicate that the acidity is due to carboxyl and not tophenolic groups.16Several interesting papers have appeared on clay, using the wordin the sense of the soil investigator, and not of the ceramic chemist.This is the fraction of soil the particles of which are 0.002 mm.or less in diameter. This has been subdivided into twenty-sixfractions by elutriation methods and each fraction fully analysed.About 80 per cent.of the total day had a fairly constant com-.position, closely approximating t'o the theoretical clay complex,A120,,2Si02,2H20. The remaining fractions, consisting of thecoarser grades, showed a gradually increasing silica content. l7A suggestive investigation which recalls some earlier work bySchloesing p&re has been published from the United States Bureauof Soils.1s Aqueous extracts of soil frequently contain a considerableamount of colloidal material, which renders them opalescent evenafter standing, and no ordinary filtration suffices to clear them.Quantities of this material have been extracted from soil andexamined; it consists mainly of hydrated silicate of aluminiumwith varying amounts of ferric hydroxide, silicic acid, organic matter,and possibly aluminium hydroxide, with small amounts of calcium,magnesium, potassium, and sodium.It showed marked colloidal pro-perties and to it is attributed much of the colloidal characteristicsof the soil. Its power of absorbing gaseous ammonia and dyestuffswas investigated, and on this is based a method for estimating theamount present in soils ; in the case examined, this was 28 per cent.,the clay on the American basis (0.005 mm. diameter) being 35.9 percent. The material is called " ultra-clay " ; it may be substantiallythe same as " clay " in the British sense (0.002 mm. diameter).Soil Acidity.Many soils are greatly improved by the addition of lime, and theobvious explanation is commonly put forward that they have insome way become acid and therefore infertile, but that fertility isrestored on neutralisation.The explanation was seriously calledin question when it was shown that absorption would account formany of the observed facts, and the tendency in recent years hasbeen to analyse the phenomena more closely.19l5 J. Marcusson, Eoc. cit.; 2. angew. Chem., 1921, 34, 437; A., ii, 590.16 Sven OdBn, Koll. Chem. Beihefte, 1919, 11, 75; A., i, 393.1 7 E. Blanck and F. Preiss, J. Landw., 1921, 49, 73.l * C. J. Moore, W. H. Fry, and H. E. Middleton, J . Iltd. E'ng. Cherri., 1921,For critical discussion, tiee E. ,4. Fisher, J . A y r i c . Xci., 1921, 11, ID;13, 527.:I., i, 215; A.Demolon, ,Inia. Sci. Agron., 1920, 37, 97.H 196 ANNUAL EEPORTS ON THE PROGRESS OF CHEMISTRY.An acid filtrate is obtained when a solution of a neutral salt ispoured through the soil. In t'he case of potassium nitrate and sodiumchloride, this has been traced to aluminium and iron rendered solubleby basic exchange; whilst in the case of calcium acetate andpotassium acetate it is due to acetic acid liberated either by re-placement of the hydrogen of hydrous silicates or by selectiveabsorption of the basic element in the salt solution.20Other causes of acidity have been investigated. It is not clear,however, that the true acidity as measured by hydrogen-ion con-centration is ever sufficient in nature greatly to affect the growthof plants.It is easy to be misled by the results of laboratoryexperiments. Degrees of acidity which proved inhibitive to micro-organisms such as Axotobacter and Actinomycetes had no observableeffect on the growth of wheat in culture solutions.21 Moreover,crops grown in sand cultures showed a higher degree of tolerance ofacidity than those grown in culture solutions.22 Indeed, sandcultures containing solutions of P,, 23 value 3 and therefore acidgave better growth than those more nearly neutral. I n the lattercase, however, the plants were chlorotic, and it is possible that thcresults are due to lack of available iron. Natural soils present evenmore complexity, since they show a high degree of buffering, whichcoarse sand doesMeanwhile, however, results are being accumulated and thequestion of method is important.The colorimetric method fordetermination of PH values is so much more rapid than the electro-metric method that it would be universally adopted if i t were equallytrustworthy. A careful examination has revealed 25 some of itsdefects and has emphasised the effect of fineness of division of thesoil.Methods of controlling the soil reaction are also being worked out.It is suggested26 that addition of sulphur to soil might produceacidity which would be useful in checking the potato scab organism(Actinomyces chromgenus, Gasperini). Good field results arerecorded, especially where the organism that oxidises the sulphuris added; the yield of potatoes was increased by 50 per cent.,whilst the percentage of unsaleable scabby potatoes fell from 58 to29 per cent.of the totalSee also J. J .Mirasol, ibid., 1920, 10, 153; A., i, 88.20 R. H. Robinson, Soil Sci., 1921, 11, 353; A., i, 644.21 H. F. A. Meier and C. F. Halstead, ibid., 1921, 11, 325.22 A. G. RlcColl and J. R. Haag, ibid., 1921, 12, 69.23 PH is the expression used for -log[H'].24 R. E. Stephenson, Soil Sci., 1921, 12, 145.2 5 E. A. Fisher, J. A g ~ i c . Sci., 1921, 11, 45.2 6 J. G. Lipman, A. L. Prince, and W. A. Blair, Soil Sci., 1921, 12, 197.27 W. 1%. Xartin, ibid., 1921, 11, 75; see also J . G . Lipman, A. W. Blair,W. H. Martin, and C. 8. Beckwith, ibid., 11, 87AGRICULTURAL CHEMISTRY AND VEGETABLE PIIYSIOLOGY. 197Another direction for utilising the acidity produced by additionof sulphur to soil is in removing the last of the alkalinity fromalkali soils after most of the salts have been washed out by irrigationwater.28The converse problem of reducing acidity by addition of lime or ofcalcium carbonate has been studied.The relationship betweenadded calcium hydroxide and P, value (as measured by electro-metric titration) is not simple,29 and some of the acid soils, forexample, in Oregon, do not respond to lime treatment.30 Noexplanation is forthcoming and further work is called for. More-over, it appears that soils contain not only calcium but magnesiumcarbonate also, and these do not behave alike.31I n general, however, acidity is rectified by addition of calciumcarbonate, and from the practical point of view it is desirable tohave some method that will show how much must be added to soilto ensure a neutral reaction.The Hutchinson-McLennan methodis shown to give useful indication^.^^ In addition to calciumcarbonate, other materials can be used ; experiments are recordedwith a slag described as ‘‘ dicalcium silicate.” 33Soil problems, however, are very complex and lime must not beregarded solely as a neutralising agent. Reference has already beenmade to the chlorosis induced in sand cultures when neutrality wasmaintained. Other observations indicate that the chlorosis inducedby lime in calcareous soils is due to depression in the availability ofiron. Evidence from ash analysis of chlorotic plants seems topoint to lack of iron as one cause of the chlorosis, a possible con-tributory cause being excess of lime (see p.208). Rice becamechlorotic in calcareous soils with ordinary percentages of water, buti t made normal healthy growth when the soil was submerged. It issuggested that special roots are formed under submerged conditionsbetter able to assimilate iron than the ordinary root.34A further effect of lime, which is often harmful, is to influence thepotash supply to the plant.35 It appears that potassium nssimila-tion by plants iw adversely affected by lime when only small amountsof potassium are present. In practice, this particular difficultlycan be overcome by supplying potassic fertilisers.Furfher, the phosphate supply is affected by calcium carbonate.2 8 P.L. Hibbard, SoiZSci., 1921, 11, 385; J. L. Lipman, ibid., 1916,2,205.29 C. 0. Swanson, W. L. Latsliaw, and E. L. Tague, J . Agric. Res., 1921, 29,30 R. H. Robinson and D. E. Bullis, Soil Sci., 1921, 11, 363 ; A., i, 644.32 Ch. Brioux, Ann. Sci. Agron., 1920, 37, 233.33 C. J. Schollenberger, Soil Sci., 1921, 11, 261.34 P..L. Gile and J. 0. Carrero, J . Agric. Res., 1920, 20, 33.35 I?. Ehrenberg, Landw. Jahrb., 1919-20, 54, 1.855.F. Hardy, J . Agric. Sci., 1921, 11, 1 ; A., i, 215198 ANNUAL REPORTS ON TfIE PROGRESS OF CHEMISTRY.The retention by soil of the P,O, of superphosphate is regarded36as a chemical interaction if calcium carbonate is present, but as aphysical adsorption if it is absent. In the former case dicalciumphosphate is formed so rapidly that the whole of the phosphate isprecipitated within a very restricted range : this becomes slowlyconverted into tricalcium phosphate.The physical adsorption in non-calcareous soils is rather differentand less rapid, so that the phosphate washes further down into thesoil.On non-calcareous soils, therefore, phosphatic manuringshould be more effective than on calcareous soils.As always happens in soil investigations, it is necessary to dis-tinguish clearly between the phenomena observed in soils devoidof vegetation and those on which plants are growing. The formerpresent the simpler case and are necessarily studied first; theplant introduces so much complication that even now little hasbeen ascertained with certainty.The relationships between soilreaction and absorption of ions are complicated in presence of thegrowing plant by the circumstance that different plants vary intheir power of absorbing nutrients from the soil: maize couldabsorb difficultly soluble phosphates from acid soils only ; mustardcould take it under more nearly neutral condition^.^'These various observations must not, however, be taken asindicating that acid soils are in general more favourable thanneutral soils for the yiclding up of nutrients to the plant. It istrue that excess of calcium carbonate seems to be harmful in somecases, but there is also evidence that plants usually obtain phos-phates more easily from neutral than from acid soils.38Effect of Salts on Soil.Just as lime has a complex action on soil SO also do various salts.There is an exchange of bases 39 which may lead to an acid reaction,as already stated. There are also important physical effects arisingout of the flocculation of clay by dissolved salts.These have beenstudied a t Rostock in an important investigation by Nolte : 40 theyhave also received attention in America. In the American investi-gations, sodium salts cause clay to become harder and less permeableto water. This is objectionable in regions where irrigation isnecessary, and in such cases the water must be examined to see if it36 W. H. Harrison and S. Das, Pusa Memoirs Chem. Series, 1921, 5, No. 9.37 M. Wrangell, Landw. Versuchs. Stat., 1920, 98, 209.38 G. S. Fraps, Texas Agric. Expt.Station Bull., 1920, 267; also 0. 11.39 For det,ails, see W. P. Kelley and A. B. Cummins, ibid., 1821, 11, 139;4O 0. Nolte, J . Landw., 1919, 67, 267.Shedd, Soil Sci., 1921, 11, 111.A., i, 388AGR.ICULTURAL CHEMISTRY AND VEGETABLE PHYSIOLOGY. 199contains more sodium and potassium than calcium and magnesium ;if so, its continued use is likely to be harmful. The suggestion ismade that addition of soluble calcium or aluminium compounds tothe water might overcome the d i f f i ~ u l t y . ~ ~Soil Analysis.One of the most difficult problems for the agricultural chemist isthat of soil analysis. He is expected to analyse soils and on thebasis of his results to give recommendations as to manuring. Un-fortunately, the problem is particularly difficult ; in most casesinsoluble on our present knowledge.The trouble arises from thefact that no two methods give the same results; it is possible fromthe Rothamsted soils to extract percentages of K20 varying from0.001 to 5 per cent., according as one extracts with water or adoptsdrastic fusion methods. Two important summaries and discussionsof the German results 42 show the relative importance there attachedto the various factors, and indicate high-pressure steam as a suitableagent in potash determinations. Another suggestion is that t,heratio of soluble to total K20 or P205 (using 1 per cent. citric acid asthe agent for soluble P205 and 10 per cent. hydrochloric acid forsoluble K20) is more useful than either figure taken separatelyin explaining fertiliser results.The authors carefully disclaim,however, any predictions of fertiliser requirement^.^^ It is suggestedalso that the plant is able to extract from a soil more K20 but lessP20, than is dissolved by 1 per cent. citric acid.The use of O*2N-nitric acid for soil analysis has been furtherdiscussed 44 and also that of hydrochloric a ~ i d . ~ 5Mechanical analysis of at present a very tedious process,promises to be simplified by using sodium carbonate as the defloccu-lating agent instead of ammonia, whilst the use of the centrifugestill further accelerates the process.47Finally, a promising attack has been made on the exceedinglydifficult problem of determining the amount of colloidal materialin soils.4841 C. S.Schofield and F. B. Headley, J. Agric. Res., 1921, 21, 265.42 J. Konig and J. Hasenbaumer, Landw. Jahrb., 1920, 55, 184; J. Konig,J. Hasenbgumer, 0. Kleine-Mollhoff, and M. L. Plouski, ibid., 1921, 56, 439.43 0. Lemmermann, L. Fresenius, and H. Wiesmann, Landw. Versuchs.Stat., 1921, 98, 155.44 0. M . Shedd, Soil Sci., 1921, 11, 111.45 F. Munter, Landw. Versuchs. Stat., 1919, 94, 181.48 For a discussion of methods, see U. Pratolongo, Ricerche R. Scuola Sup4 7 A. F. Joseph and F. J. Martin, J . Agric. Sci., 1921, 11, 293.48 C. J. Moore, W. H. Fry, and H. E. Middleton, J. Ind. Eng. Chern., 1921,d’Agric. di Milano, 1920, 6, 97.13, 527; A., ii, 608200 ANNUAL REPORTS ON THE PROGRESS O F CHEMISTRY.hydration or water of solid solution ; unavailableEnvironmental Conditions.A detailed study of soil temperatures 49 brings out the interestingfact that the top 6 inches of soil is on the whole rather warmer thanthe air, so that the temperature conditions are more favourable tomicro-organisms and plant roots than might be expectedAGRICULTURAL CHEfiIIYTRY AND VXGETABLE PHYSIOLOGY. 201tration of cell sap has been shown to depend on the moisture contentof the soil; apparently this is the chief factor concerned.A lowconcentration (induced by high moisture content) is associated withrapid vegetative growth ; a high concentration with slower growthbut with fruit bud f o r m a t i ~ n . ~ ~Soil Organ is rlzs.The relationships existing between the growing plant and themicro-organic population of the soil are gradually being elucidated,56but the papers published this year deal largely with matters ofdetail.The range of substances decomposable in thc soil bymicro-organisms is remarkable, and includes some of the verystable hydrocarbons such as paraffins, benzene, toluene, etc. ; 57i t is even suggested that soil organisms could be used in gas analysis€or discriminating between certain hydrocarbons.Most of the investigations, however, deal with the nitrogen cycle.Many organisms are capable of decomposing protein with formationof ammonia; it is not usual to discriminate between these in soilinvestigations, but only to count them; a comparison has beenmade of different counting methods adopted. 58I n nature, the ammonia is almost invariably oxidised bacteriallyto nitrate, and attempts have several times been made in France toutilise this action on the manufacturing scale : a new method issuggested in which ammonium salts percolate through peat orvolcanic scoriae.59The bacterial fixation of nitrogen continually attracts attention :i t is effected by two groups of organisms, Axotobacter and Clostridium.The former is usually regarded as the more important ; i t assimilatesnitrogen more slowly at ordinary laboratory temperature than at27", but fixes more per unit of mannite consumed.60 The effectsof coloured light and of uranium salts have also been studied. Ainethod of estimating the numbers of Clostridium in the soil hasbeen devised,61 and the view is put forward that i t is more numerousthan Axolobacter and probably p-'li~ys a more important part in thefixation of nitrogen.65 H. S.Reed, J. Ryric. Bes., €921, 21, 81.56 For a recent summary, see E. J. Russell, Ann. Sci. Agron., 1921, 38, 49.57 J. Tausz and M. Peter, Centr. Bakt. Par., 1919, [ii], 49, 497; A., 1920,58 Z. N. Wyant, Soil Sci., 1921, 11, 295.59 E. Boullanger, Ann. Inst. Pasteur, 1921, 35, 575; A., i, 836.6O E. Kayser, Cornpt. rend., 1920, 171, 969; A., i, 79; ibid., 1921, 172,1Y3, 403, 939, 1133; A . , i, 208, 479.61 G. 'I'ruffaut and N. Bezssonoff, ibid., 1921, 172, 1319.i, 911.11 202 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.A third group of organisms acts in symbiosis with leguminousplants and is closely related in activity to the growth of the plant.62Morphologically they present many features of interest.63Other organisms seem concerned in the loss of nitrogen from soil,some of which is presumably brought about by an evolution ofgaseous nitrogen. Although little is known of the mechanism ofthe process, further measurements have been made of the quantitiesinvolved. In the New Jersey cylinder experiments, which extendedover a period of twenty ~ e a r s , ~ 4 the loss has usually been of theorder of 100 lb. per acre for the first fifteen years; where, however,green manure was used, there was no loss, but a gain.Partial Xterilisation.Further results have been published65 showing the increase ofcrop yield resulting from heat treatment of soil. The effectspersisted for several crops ; they varied somewhat, however, withthe different layers of soil.The introduction of untreated soil didnot wholly counteract the effect of steaming, showing that thedecomposition of soil materials is a potent factor in determiningthe effect.Owing to the cost and limited application of heat, efforts arecontinued to find some chemical agent capable of modifying thesoil population in the desired direction. Studies have been madeof p-dichlorobenzene, which gave promising results against thePeach-tree Borer (Sanninoidea exitiosa, Say), a destructive pest ofpeach trees,G6 and of the physical and other conditions affecting theuse of carbon disulphide as a soil sterilising agent.67Phenol has also proved effective, but it is liable to certain obscureinteractions with soil constituents and to biochemical decompositionin the soil whereby its value is much diminished.68Chloropicrin and formaldehyde are useful partial sterilisingagents,69 and their effect on germination has been discussed.7062 A.L. Whiting and W. R. Schoonover, Soil Sci., 1920, 10, 441.63 F. Lohnis and R. Hansen, J . Agric. Res., 1921, 20, 543.64 J. G. Lipman and A. W. Blair, Soil Sci., 1921, 12, 1.65 Viscount Elveden, J . Agric. Sci., 1921, 11, 197.6 6 A. Peterson, Soil Sci., 1921, 11, 305.6 7 B. R. Leach, ibid., 1921, 10, 421.6 8 N. N. Sen Gupta, J . Agric. Sci., 1921, 11, 136.69 E. J. Russell, J . Roy. Hort. SOC., 1920, 45, 237.70 E. Mihge, Compt. rend., 1921, 172, 170 (chlaropicrin); A.H. Hurd, J.Agric. Res., 1920, 20, 209 (formaldehyde)AGRICULTURAL CHEMISTRY AND VEGETABLE PHYSIOLOGY. 203T h e C h e m i s t r y of t h e Living P l a n t .Photosynthesis.The rapid production of sugar in the leaf from carbon dioxidecontinues to evoke a great volume of research. Baeyers’ originalhypothesis still holds the field, and there is no generally recognisedalternative to the view that the first product is formaldehyde, whichsubsequently condenses to sugar. The key-sugar in carbon ineta-bolism, both in the up- and the down-grade processes, appears tobe glucose. The pentoses, however, are invariably present andplay an important part in plant processes, entering into the com-position of the nucleus, of certain cell-walls and of mucilage,71and helping considerably in determining succulence.72Numerous investigations have shown that formaldehyde is obtain-able in circumstances more or less comparable with those obtainingin natural photosynthesis. The more notable papers include onefrom a physico-chemical laboratory where the chemical pitfalls areavoided,’3 and one from a physiological laboratory where the plantconditions are fully re~ognised.~~ In the latter it is claimed thatthe production of formaldehyde results from the decomposition ofchlorophyll and is not directly dependent on the presence of carbondioxide. An interesting discussion, which, moreover, invitescontroversy, is contained in the Hugo Muller lecture.75 An alterna-tive view is put forward by Maze in which the principal part isassigned to hydroxylamine.This base is supposed to arise in theleaves by reduction of nitric acid (nitrates being the recognisednitrogenous nutrients of plants and absorbed in considerablequantities from the soil); i t combines with carbon dioxide aridchanges as follows :C02,NH2*OH = H*CHO + HNO,,also 2C02,NH2*OH = CH,(OH)*CHO + ZHNO,.These products are actually found in the leaves of the elder.The glycollaldehyde may become reduced to acetaldehyde ; thisreacts to produce lactaldehyde and nitrous acid,CH,*CHO + C02,NH2=OH = CH,*CH(OH)*CHO + HNO,,71 F. F. Blackman, New Phytologist, 1921, 20, 2.72 H. A. Spoehr, “The Carbohydrate Economy of the Cacti,’’ Carnegie73 E. C. C. Baly, I. M. Heilbron, and W. F. Barker, T., 1921, 119, 1025.74 W.J. V. Osterhout, Amer. J. Bot., 1918, 5, 511; A., i, 263.75 B. Moore, T., 1921, 119, 1555.Inst. Pub. No. 287, 1919.lp: 204 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.which occur in the leaves of the poplar. It is not difficult in thisway to build up substances of any desired degree of elab~ration.~~Whatever view is taken as to the actual course of photosynthesis,it is known that potassium plays an important part, although thereis not necessarily a specific effect. It is shown that wheat canproduce and translocate a certain amount of starch in presence ofonly little of this element.77 It does not appear that the potassiumis in organic combination in the plant, since it can all be extractedwith water. 78Iron also has always been regarded as essential for the productionof chlorophyll.It is now maintained that the magnesium salt ofpyrrolecarboxylic acid serves instead, and in culture solutionsdetermines the formation of chlorophyll even in absence of iron.It is therefore suggested that the function of iron in the leaf is toact as catalyst in the formation of pyrrole, which is regarded as thecentre of the chlorophyll complex. 79Other inorganic nutrients are essential to plant growth, andspecial importance has always been attached to nitrogen, potassium,and phosphorus because of the striking results obtained by the useof their compounds as fertilisers. Attempts have been made tofind quantitative relationships between the amounts of plantnutrients supplied and of the subsequent plant growth.The oldidea that growth was proportional to the quantity of fertiliser hadlong ago to be abandoned; it was followed by Mitscherlich's viewthat the effect of a nutrient salt (or other factor) is proportional tothe decrement from the maximum obtainable when that salt orfactor is present in ample quantity. This view has the merit thatit is readily expressible in the form of a logarithmic equation, theconstants of which hold out attractive possibilities for the agricul-tural chemist; it has, however, evoked a storm of criticism inGermany,g0 and in any case it appears to be too simple a statement,as the results are more readily expressible by a sigmoid than by alogarithmic curve. 81171, 1391; A., i, 151.7 6 P.Maz6, Compt. rend., 1921, 172, 173; A., i, 209. See also ibid., 1920,77 T. 0. Smith and 0. Butler, Ann. Bot., 1921, 138, 189; A., i, 482.76 S. Kostychef and P. Eliasberg, 2. physiol. Chem., 1920, 111, 228; A.,'9 B. Odd0 and G. Polacci, Gazzetta, 1920, 50, 54; A., 1920, i, 407.i, 83.Among recent papers are A. Mitscherlich, Landw. Jahrb., 1921, 56, 71 ;B. Baule, ibid., 1920, 54, 493; A. Mayer, Landw. Versuchs. Stat., 1919, 94,247. For a useful r6sum6, see E. Lang, Landw. Jahrb., 1920, 55, 337.81 Rothamsted Report, 1918-20, p. 14; A. Rippel, Landw. Vemuchs.Stat., 1921, 9'9, 357. For a discussion of the distinction between growthrate and h a 1 growth, see C. West, G. E. Briggs, and F. Kidd, New Phytologist,1920, 19, 200AGRICULTURAL CHEMISTRY ANT) VEGETABLE PHYSIOLOGY.205There has been much discussion, initiated by Shive and Totting-ham's earlier work, as to the need for some definite physiologicalbalance 'between the various plant nutrients ; it is, however, shown 82that there isno " best " solution for plant growth : aconsiderablerangeof mixtures is possible, although " poor " solutions can be made.s3Some proportionality between CnO and MgO seems indicated byconsideration of the analyses of plant a ~ h . ~ 4 A detailed study ofthe potato in sand cultures is also rep0rted.~5Further, it is possible to effect disturbances in plant nutritionby altering the course of absorption of the nutrients. Assimilationbecomes abnormal when a plant root is divided among severalnutrient solutions from each of which one essential nutrient iswithheld.It is suggested that the cause lies not so much with theactual absorption of the nutrient as with the subsequent transloca-tion, and values have been calculated for nitrogen, phosphoric acid,and potassium which show a reasonable measure of agreement withthe results actually found.86The older agricultural chemists confined themselves almostexclusively to the three nutrients nitrogen, phosphorus, and potass-ium; of recent years, however, the French chemists have directedattention to the importance of other elements. Berfrand firstinsisted on the importance of manganese and now shows 8' that itis invariably present, the supposed exceptions of Maumene beingnon-existent. Copper is shown to be invariably present in plants;it is subject to translocation and migrates t o points of greatestvitality as if it played an active part in intracellular metabolism.88Iron presents a somewhat more complex problem, since it existsin the plant in two forms which are not readily distinguished : a8Fe,03 deposited by evaporation in the leaf or absorbed in the cellularrnembrane~,~~ and as an organic complex comparable with Bunge'shaematogen ; the latter becomes translocated and moves towardsthe centres of active life and reprod~ction.~~62 A.R. Davis, Soil Sci., 1921, 11, 1.Confirmed also by L. H. Jones and J. W. Shive, J . -4gric. Res., 1921,21, 701.84 H. Lagatu, Compt. rend., 1921, 172, 129; A., i, 214.8s E. S. Johnston, XoiZ Xci., 1920, 10, 389.E 6 P.L. Gile and J. 0. Carrero, J . Agric. Res., 1921, 21, 545.G. Bertrand and Mme M. Rosenblatt, Compt. rend., 1921, 173, 333;A., i, 759; J. S. Jones and D. E. Bullis, J . Ind. Eng. Chem., 1921, 13, 524;A., i, 840. For a soil study, see P. Nottin, Ann. Sci. Agron., 1920, 37, 228.See alsoa suggestive paper by these authors in Ann. Xci. Agrom., 1921, 38, 113.For this inorganic iron, see H. W. Jones, Biochem. J . , 1920, 14, 654;A., 1920, i, 909.L. Maquenne and R. Cerighelli, Cornpt. rend., 1921, 173, 273; A., i, 759.8 8 L. Maquenne and E. Demoussy, Compt. rend., 1920, 170, 87206 ANNUAL REPORTS ON THE PROGRESS OF CHEMISTRY.A study of iron nutrition has shown that the availability andsufficiency of a particular iron compound depends on the otherconstituents of the nutrient solution and on its hydrogen-ion con-~ e n f r a t i o n .~ ~ Thus ferric phosphate was of little value to plantswhen the nitrogenous nutrient was a nitrate; but it was quiteeffective when ammonium sulphate was used. On the other hand,ferrous sulphate was effective in presence of nitrates, but toxicwhen used in conjunction with ammonium sulphate.Pot experiments suggest that small doses of boric acid cause anincrease in plant growth, but it is not clear that crop increases areproduced in the field. The subject is of some importance in America,because boron occurs in some of the naturally occurring potassiumsalts which have been proposed for use as fertiliser ; it is found that3 to 5 lb. per acre is the largest permissible dose of anhydrous borax,and there was no evidence of any beneficial effect with this or smallerquantities .92Finely powderedsulphur, when added to soil in certain cases, increases plant growth ;the action is considered to include a t least three factors; some ofthe sulphur is oxidised by bacteria to sulphuric acid, which bringsinto solution more phosphate, potassium, etc.; it seems to stimulatethe activities of the ammonifying, the nitrifying, and the noduleorganisms ; and apparently 93 it stimulates the production of starchin plants.Possibly some such action may explain the curious observationthat beans germinated and grown in distilled water became etiolatedand died for want of food, whilst large reserves still remained in thecotyledons.On the other hand, growth continued in soil andexhaustion of reserves was much more complete.g4It is probable that all these effects are complex.Plant Constituents.This branch of the subject belongs properly to organic chemistry,and only brief reference will be made to it here. The fundamentalproduct is starch, but its transformations cannot be followed withcertainty because no satisfactory method exists for its determinationn plants. Taka-diastase converts it into maltose and dextrose only,and was therefore proposed 95 as a suitable analytical agent ; it nowappears,96 however, that this substance does not give concordant1921, 11, 93.91 L. R. Jones and J. W. Shive, J. Agric. Res., 1921, 21, 701; Soil Sci.,92 J. R.Neller and W. J. Morse, Soil Sci., 1921, 12, 79.93 G. Nicolas, Cornpt. rend., 1921, 172, 85.94 G. D. Buckner, J . Agric. Res., 1921, 20, 875.95 W. A. Davis and A. J. Daish, J . Agric. Sci., 1914, 6, 152.96 E. Horton, {bid., 1921, 11, 240AGRICULTURAL CHEMISTRY AND VEGETABLE PHYSIOLOGY. 307results, and indeed doubt is expressed whether any ordinary enzymewould do so. Until he can follow the more important changes in thegrowing plant, the agricultural chemist is not as a rule directly con-cerned with questions of constitution of these various constituent^.^^The nitrogen compounds in plants are steadily being investigated.A method is suggested for extracting the protein from leaves byuse of water saturated with ether.98Nitrogen compounds have been extracted and examined fromlucerne ~eed,~9 pecans, peanuts, and kafir,l mungbean (Phaseolusaureus, Roxburgh), coconut 3 (Cocus nuciferu), cohune nut (AttaleaCohune),* and the egg plant (Solanurn melongem, L.).6Some work has also been done on the formation of alkaloids.6Annett has continued his studies of the morphine content ofpoppies and has made a survey showing the quantity of opiumproduced from this crop in the more important districts in India.That most remarkable of all chemical processes, the synthesis ofnitrogen compounds from gaseous nitrogen in the nodules on theclover root, has been further examined but not yet elucidated; 8about 60 per cent.of the soluble nitrogen in the nodules of soy beanis precipitated by phosphotungstic acid ; apparently, however, noglobulin is present and only a smaU amount of albumin.9 Fieldexperiments show the great advantage of inoculation for soy beans,and on certain soils, for canning peas.1°s7 Among the papers are : “ Starch,” M.Samec and R. Haerdtl, Koll.Chem. Beihefte, 1920, 12, 281; A., i, 226; P. Karrer et al., Helu. Chim. Acta,1921, 4, 678; A., i, 768. “Cellulose,” K. Hess, Helv. Chim. Acta, 1920, 3,866; &4., i, 12; P. Karrer and F. Widmer, ibid., 1921, 4, 174; A., i, 310;M. Samec and J. Matula, Koll. Chem. Beihefte, 1919, 11, 37; A , , i, 397;K. Freudenberg, Ber., 1921, 54, [B], 767; A., i, 400; A. Cleve von Euler,Chem. Ztg., 1921, 45, 977; A., i, 769. “ Wood,” H. Wislicenus, Kolloid Z.,1920, 27, 209; A., i, 84; F.Lenze, B. Pleus, and J. Miiller, J . pr. Chem.,1920, [ii], 101, 213; A., i, 163.98 A. C. Chibnall and S . B. Schryver, Biochem. J . , 1921,15, 60; A., i, 482.ss H. G. Miller, J . Amer. Chem. SOC., 1921, 43, 906; A., i, 486; see alsonext reference.C. T. Dowel1 and P. Menaul, J . Biol. Chem., 1921, 46, 437 ; A . , i, 644.C. 0. Johns and H. G. Waterman, ibid., 1920, 44, 303; A., i, 84.D. B. Jones and C. 0. Johns, ibid., 291; A., i, 66.C. 0. Johns and C. E. F. Gersdorff, ibid., 1920, 45, 57; A., i, 212.Kiyohisa Yoshimura, J . Chem. SOC. Japan, 1921, 42, 16; A., i, 296.See G. Ciamician and C . Ravenna, Atti R. Accad. Lincei, 1920, [v], 29,7 H. E. Annett, H. Das Sen, and H. DayalSingh, Puea Memoire Chem.For further details of the facts, see A.L. Whiting and W. R. Schoonover,W. H. Stroud, ibid., 1921, 11, 123; A , , i, 387,i, 416; A., i, 85.Sem’m, 1921, 6, No.1; H. E. Annett, Biochem. J . , 1920, 14, 618; A., i, 87.Soil Sci., 1920, 10, 411.10 E. B. Fred, ibid., 469, 479208 ANNUAL REPORTS ON THE FROGR12SS OF C’HEMTSTR’T.The function of hydrocyanic acid has been discussed, but nodefinite conclusion i cachcd.llColowing 31aterials in Plants.The only colouring material of agricultural interest is indigo,which is still grown to an important extent in India. There is somecontroversy as to the conditions under which the greatest productionof indican is obtained; A. and G. L. C. Howard l2 maintain thatthe yield is improved by organic manures, but not particularly bysuperphosphate ; whilst W.A. Davis insists that phosphates areof prime importance.The admirable discussion on colouring materials in plants givenby Prof. R. Robinson before the British Association a t Edinburghis of very great interest to agricultural chemists.Calcifuges and Calcicolous Plants.Plants which fail to grow on calcareous soils are called calcifuges,whilst those which occur there more frequently than on other soilsare described as calcicolous. The cause of the difference is obscure(see p. 197), but a promising mode of study has been opened up byM. C. Rayner,13 which offers possibilities considerably in advanceof anything hitherto available. A technique has been devised forgrowing a typical calcifuge Calluna and its associated fungusseparately in culture solutions.It is shown that Calluna will grownormally in an aqueous extract of a non-calcareous soil, whiIst itfails to make such good growth in the extract of a calcareous soil.Clearly, therefore, the soil factor concerned is not exclusivelyphysical, since it is transmitted to the extract ; it does not appear tobe concerned entirely with the reaction, since the favourable extractwas neutral and the unfavourable one only slightly alkaline. Itshould not prove impossible to trace the cause of the unsuitabilityof the extract of calcareous soil.Fertilisers.As in past years, this branch is dealt with fully in the Report tothe Society of Chemical Industry, and only brief reference will bemade here to features of special interest.The problem of increasing the supply of organic matter in the soil11 L. Rosenthaler, Schweiz. ApotL-Zeit., 1920, 48, 137; 1921, 49, 10, 22;12 Pusa Mem. Bot. Series, 1021, 11, No. 1.1s 31. C. Rnyner, J . EcoEogy, 1921, 19, GO.A., i, 484; P. Menaul, J. Biol. Chem., 1921, 46, 297; A . , i, 484AGRICULTURAL CHEMISTRY ANT) VECTETARLTC PHVSIOLOCIY. 209has been attacked by ascertaining the conditions under whichstraw decomposes to form humus, and then carrying out the decom-position on the farm. The necessary conditions are, air and watersupply, a nitrogen nutrient for the organisms effecting the decom-position, and sufficient calcium carbonate to ensure neutrality. Itis claimed that an effective fertiliser can be produced from straw inthis way, and that the process can be worked on farms where in-sufficient farmyard manure is obtained during the ordinaryoperations .I4Nuch interest has been aroused in technical circles by theannouncement in Germany that artificial enrichment of the atmo-sphere in carbon dioxide was being practised successfully as a meansof increasing plant growth both in glasshouses and in the open.A patent has been taken out for absorbing this gas from flue andfurnace gases, then evolving it and delivering it in pipes near to thcroots of plants. So much interest has been aroused that themethod will probably be tested in this ~ 0 u n t r y . l ~E. J. RUSSELL.1 4 H. B. Hutchinson and E. H. Richards, J. Min. Agric., 1921, 28, 398.F. Bornemann, “ Kohlensaure und Pflanzenwachstum,” Parey, Berlin,1920; F. Riedel, Stuhl u. Eisen, 1919, 40, 1497; Mdllers Deut. Gartner Ztg.,July 20 and 30, 1921, where some illustrations are given; Chem. Ztg., 1920,585, 808