March 1, 1894.] 



KNOWLEDGE. 



69 



Dr. (now Sir) J. Gilbert have carried on an elaborate 

 series of investigations in scientific agriculture at 

 Eothampstead, which has made that little place famous 

 and has earned for the authors a world-wide renown. 

 In the course of then- numerous experiments they 

 found that in the case of leguminous crops, such as 

 peas, beans, and vetches, it was impossible to account 



Fia. 2. — BlocV made from a photograph of Hoots of ]ioorlv gi'o«Ti 

 Pea-plauts, \vith badly-dereloped uodales. 



in the usual way for the whole of the nitrogen con- 

 tained in them. It was in excess of what could have 

 been derived from the rain or the combined nitrogen 

 of the soil supplied in the manure. An examination of 

 the root? of these plants, moreover, invariably disclosed 

 the presence of nodules of various sizes and in varying 

 quantities, and a chemical analysis of these tubercles 

 showed them to be rich in nitrogen, and at certain periods 

 teeming with minute organisms, whose life-history we 

 shall presently discuss. Fig. 2 is a reproduction of an 

 actual photograph of the roots of some pea-plants on which, 

 unfortunately, the nodules are very small. The nitrogen 

 of the air can be the only source of this extra supply of 

 nitrogen, yet for years past it had been strenuously denied 

 that green plants have the power of making use of this 

 vast inexhaustible reservoir. These results, however, of 

 two of the experimenters, startling in the extreme, again 

 brought up the question of nitrogen fixation, and it was 

 attacked by such men as Berthelot, Hellriegel, Wilfarth 

 and Warrington. A paper from the pen of Lawes and 

 Gilbert appears in the Transactions «/' the Eoi/al Societi/ 

 for 1890. It commences with a summary of the results 

 obtained up to that time. " In prenous papers, of all the 

 various results discussed, those of Hellriegel and Wilfarth 

 were considered to be by far the most definite and 

 significant ; pointing to the conclusion that, although 

 the higher chlorophyllous plants may not directly use the 

 free nitrogen of the air, some of them, at any rate, may 



acquire nitrogen brought into combination under the 

 influence of lower organisms, the development of which is, 

 apparently, in some cases always coincident with the 

 growth of the higher plant whose nutrition they are to 

 serve." The authors then instituted experiments with a 

 view to confirm these conclusions. They state that these 

 have amply confirmed the results of Hellriegel, and that 

 the fixation of fi-ee nitrogen by the growth of the 

 LeguminosiB under the influence of microbe seeding of 

 the soil, and the resulting nodule formation on the roots, 

 may be considered as fully established. 



It is thus seen that the excess of nitrogen cannot be 

 explained by any of the commonly received theories of vege- 

 table physiology we have in outline explained, and also that 

 the importance of this source of nitrogen cannot be over- 

 estimated fi'om an economical point of view. It would 

 take us beyond the limits of our space to give in anything 

 like an intelligible manner the life-history of the organism 

 to whose growth the formation of these nodules is due. 

 Next month we shall give in detail the facts so far as 

 known, and illustrate these with reproductions from the 

 original drawings of Prof. Marshall Ward, who has fully 

 worked out the subject. 



Li the meantime we would briefly call attention to the 

 important practical bearing of the facts known in coiniection 

 with the formation of these tubercles. Two or three years 

 ago. Prof. Vnies, in a paper in the Annals of Botanif, 

 gave some statistics embodying the results of experiments 

 undertaken to show the influence of the chemical character 

 of the surroundings on tubercle formation. From these it 

 appears that if there is a copious supply of nitrogen in the 

 form of soluble salts, no tubercles, or at least only a few, 

 are formed. And Lawes and Gilbert state, in the paper 

 already referred to, that the evidence of experiments seems 

 to indicate that there is a less development of nodules when 

 the soil is rich in combined nitrogen ; while Hellriegel, 

 who agrees that leguminous plants do make use of soil 

 nitrogen, considers that by the aid of the tubercle-forming 

 organisms they draw upon the free nitrogen supplied by 

 the air, and that the formation of the tubercles is, within 

 certain limits, inversely proportional to the supply of com- 

 bined nitrogen in the soil. It appears that something like 

 this at least is the case, and we can at once see how im- 

 portant is a knowledge of the process going on from an 

 agricultural point of view. At present agriculture in 

 England is in a precarious condition, in which any know- 

 ledge which may lead to an economy in the supply of 

 manure will be welcomed. The most expensive manures 

 are generally those containing nitrogen, manures such 

 as nitrate of soda and farmyard manure. Tha latter, 

 however, contains only a small percentage of nitrogen 

 in a readily available form. Heavy clay soils and very 

 porous soils would not be much benefited by the 

 application of artificial nitrogenous manures, as they 

 require that added, which will make the one less and the 

 other more tenacious in character. But although farm- 

 yard manure is cheap in itself, yet the cost of putting it on 

 the soil is considerable, especially if a large area has to be 

 treated ; but in such cases the growth of leguminotis crops 

 may be resorted to. To quote from the Gardeners' Chronicle 

 of 7th May, 1892 ;— 



" In our own comitry Mr. Mason, of Eynsham Hall, 

 Oxfordshire . . . has devoted about two hundred acres 

 to the practical application of the recently- acquired know- 

 ledge in regard to nitrogen fixation. Stated in a few words, 

 this idea is to reduce the area under roots and to grow 

 instead mixed crops of Leguminosie — beans, various clovers, 

 &c. — liberally manured with basic slag and kainit (manures 

 which contain phosphorus and potassium especially) and 



