332 



NATURE 



[August 1, 1889 



before we reach the Mississippi River the ratio is reduced 

 to 1-32. 



In Great Britain the amount of rain with a falling is twice that 

 with a rising barometer, but, advancing eastward, this ratio 

 rapidly diminishes, and in Central Europe the precipitation is 

 greater when the barometer is rising than when it is falling. 

 Plates are appended, which exemplify in an emphatic manner 

 all the facts that have been tabulated concerning rainfall. Five 

 gradations of colour only have been used to indicate the rain- 

 fall of less than 10 inches to over 75 inches. By this means the 

 main results have been rendered more prominent. 



R. A. Gregory. 



THE SOURCES OF THE NITROGEN OF 

 VEGETATION.^ 



IVrO problem relating to the nutrition of plants has given rise to 

 so much discussion as that of the source of their nitrogen 

 and the methods of its assimilation. It is obviously both a matter 

 of the highest scientific interest, and also, owing to the high 

 price of combined nitrogen in manures and the comparative ease 

 with which it is washed out of the soil in the form of nitrates, 

 one of great practical importance to the agriculturist and the 

 community. 



Ever since the discovery of the composition of atmospheric air 

 by Priestley, Scheele, and Lavoisier, the question as to whether 

 plants were able to absorb and "utilize free nitrogen has attracted 

 much attention. At the end of the last century, or beginning of 

 this, Ingenhousz, Sennebier, Woodhouse, and De Saussure 

 became interested in the subject. 



Boussingault commenced his experiments in 1837 ; Ville, 

 whose results conflicted with those of Boussingault, in 1849 ; and, 

 shortly after, this last named investigator started a new series of 

 experiments which confirmed his former conclusions that plaits, 

 under the conditions of the experiment, were not able to 

 assimilate free nitrogen. 



In 1857, experiments on the assimilation of free nitrogen by 

 plants were started at Rothamsted ; and in 1861 was published, 

 in the Philosophical Transactions, the classical memoir of Lawes, 

 Gilbert, and Pugh, on this subject. 



In this earlier paper a brief history and summary otthe results 

 of other experimenters is given, and then the recent results 

 obtained at Rothamsted. The conclusions arrived at were 

 identical with those of Boussingault, that there is no evidence 

 that plants assimilate nitrogen. Still the authors allowed that 

 there were some difficulties with regard to the supply of nitrogen 

 to leguminous plants, which assimilate from some source or 

 another much more nitrogen than gramineous plants under similar 

 conditions of supply of combined nitrogen. 



It was admitted that, "if it be established that the processes 

 of vegetation do not bring free nitrogen into combination, it still 

 remains not very obvious to what actions a large proportion of 

 the existing combined nitrogen may be attributed." 



_ These views, that plants were unable to assimilate free 

 nitrogen were widely and generally held for many years, though 

 there have always been some dissentients. 



In the meantime, however, the indefatigable investigators of 

 Rothamsted have not been resting in the matter, but have added 

 much to our exact knowledge of the supplies of combined 

 nitrogen to the soil from the air, on the amount and nature of 

 the combined nitrogen in soils and in crops, on the processes of 

 •nitrification in soils, and the amount of nitrogen removed from 

 soils in crops and in drainage. 



During the last few years the main question as to the availability 

 of atmospheric nitrogen to p'ants has taken a somewhat different 

 aspect : it is now often suggested that though the higher plants 

 ■are unable to directly take up free nitrogen, yet indirectly it is 

 brought under contribution in some way ; the ways most 

 generally favoured being either under the influence of elec- 

 tricity of low tension, or of microbes or some low forms of 

 organisms ; and by such means it is thought that nitrogen 

 is brought into a form in which it is useful to the higher 

 plants. 



In Sir J. B. Lawes and Dr. Gilbert's new memoir they give a 

 summary of some previously published Rothamsted results, 



' " On the Present Position of the Question of the Sources of the Nitrogen 

 •of Vegetation, with some New Results, and Prehminary Notice of New 

 Lines of Investigation." By Sir J. B. Lawes and Prof J. H, Gilbert. Phil. 

 Irans. 1889, clxxx. B. pp. 1-107. 



chiefly relating to nitric acid in soils and subsoils ; also of the 

 results of Cameron, S. W. Johnson, Hampe, Wagner, and 

 Wolff, on the assimilation of nitrogen by plants, from more or less 

 complex organic bodies like urea, uric acid, hippuric acid, and 

 tyrosine. 



A number of new determinations of nitric acid in soils and 

 subsoils, and of total combined nitrogen in the surface soils of 

 the Rothamsted experimental plots are given ; and also the 

 results of numerous experiments with dilute solutions of organic 

 acids on soils, to ascertain the action of such dilute r cids, in some 

 degree comparable to the acid sap of the roots of plants, on the 

 organic nitrogenous matter of soils. 



In the second part of the memoir are summarized the recent 

 results and conclusions of other workers relating to the fixation 

 of free nitrogen. 



Probably the results of Berthelot, which have from time to 

 time been published in the Coiiiptes rendus, have influenced the 

 opinions and the course of inquiry in recent years more than any 

 others. In 1876 and 1877, Berthelot found that various organic 

 compounds under the influence of the silent electric discharge, 

 even of low tension, were able to fix free nitrogen, and concluded 

 that such fixation of nitrogen takes place in ordinary soils under 

 normal conditions. In 1885 he published results showing the 

 fixing of free nitrogen by certain sails under conditions which 

 led him to believe that the action must be due to the influence 

 of micro-organisms, and to such action M. Berthelot seems now 

 inclined to impute most influence in the matter. Although the 

 gains in nitrogen, expressed in percentages, were very small, yet 

 there was gain in all cases when the soils were exposed either 

 in the open, or in a room, or in closed flasks, and no gain when 

 the soils were sterilized. Unless there be some unrecognized 

 source of error, such as might easily be imagined in the case of 

 the freely exposed soils, one seems bound to accept Berthelot's 

 conclusions. Deherain's results at Grignon are next discussed ; 

 they are chiefly on the gains or losses occurring on experimental 

 field plots, and are perhaps not of such a nature as to materially 

 assist one at the present stage of the inquiry. 



Joulie's results, as given in the Btilletin de la Socicte des 

 Agrictdtetirs de France in 1886, showed exceedingly large gains 

 of nitrogen, which he is inclined to ascribe to the action of 

 microbes ; here the gains of nitrogen were certainly more than 

 take place in ordinary farm practice, and occurred with buck- 

 wheat, which is not usually considered as a " nitrogen collector." 



Dietzell's experiments are mentioned ; in all cases but one, 

 in which there was a slight gain in nitrogen, the results are fully 

 accordant with established facts. B. F"rank, who has recently 

 written a paper on the whole aspect of the question, has pub- 

 lished some experiments of his own. He concluded, as have 

 others, that two opposite actions are at work in the soil — one 

 setting nitrogen free, and the other bringing it into combination, 

 the latter being favoured by vegetation — but that there is no 

 decisive evidence to show how this combination is brought about ; 

 it does not necessarily follow that the plant itself effects the 

 combination. Some of Frank's experimental conditions, how- 

 ever, were considerably removed from those occurring in the 

 ordinary course of farm practice. 



The very important and most interesting experiments of 

 Hellriegel and Wilfarth follow. The first of these were de- 

 scribed at the Berlin meeting of the Nahirfovschei-- Versammlung, 

 in 1886 ; subsequent experiments were described at the Wiesbaden 

 meeting in 1887, and they were further given in a paper by 

 Konig, published in Berlin in 1887 ; but the full text and details 

 of their work were not published in time for Messrs. Lawes and 

 Gilbert to refer to. A paper on these results appeared last 

 November in Beilageheft zu der ZeitscJirift des Vereins fiir 

 die Rubenzucker-Industrie, and the work of these investigators 

 is described by M. Vesque in the January number of Annates 

 Agronomiques . 



The experiments date from 1883 onwards, and were on 

 cereals, buckwheat, rape, and various leguminous plants. The 

 plants were grown in pots in washed siliceous sand, to which 

 the necessary cinereal constituents were added. In this all the 

 plants grew normally until the nitrogen in the seed was used 

 up ; then the plants not belonging to the Leguminosce ceased 

 growing until supplied with some combined nitrogen, nitrate of 

 soda was used, when growth was proceeded with almost exactly 

 in proportion to the amount of nitrogen supplied. With the 

 Leguminosae the results were more eccentric : sometimes thfl 

 plants died of nitrogen-hunger ; sometimes after a lime oj 

 such hunger they recovered and produced abundant growth. Tf 



