42 



NA TURE 



[May 8, 1890 



soil in the case of all the plants except the lupins, and for these 

 from a special sandy soil from a field in which lupins were grow- 

 ing. No. 4 garden soil, or, for the lupins, the special lupin soil. 

 With regard to the peas and vetches of the pots not seeded with 

 soil extract, the growth was extremely limited, and the colour of 

 the leaves pale green ; in the second and third pots of the two 

 series there was luxuriant growtTi, the plants being taller even 

 than those grown in garden soil. On the other hand, the garden 

 soil plants were more vigorous and produced flower and seed. An 

 •examination of the roots of the plants showed an entire absence 

 of nodule formation on those of the pots where no soil extract 

 ■was given, whilst on the roots of the other plants there was, 

 coincidently with the increased growth, an abundance of nodules. 

 As in the experiments of 1888, the amount of nodules on the roots 

 of the plants grown in garden soil was less than in the sand 

 treated with soil extract. 



Still more striking were the results obtained with yellow lupins. 

 Whilst the plants of pot i (without soil extract) barely appeared 

 tibove the rim of the pot, those of pots 2 and 3 (with soil extract) 

 were large branched plants, the largest being 2 feet high — larger 

 even than those grown in the lupin soil. Moreover, unlike the 

 peas and vetches, the yellow lupins grown in sand seeded with 

 soil organisms, flowered and seeded freely. The superiority of 

 these plants over those grown in the lupin sandy soil may be due 

 to the fact that the lupin soil was much less porous than the 

 sand, especially when watered, and perhaps on this account less 

 adapted for favourable growth. The roots of the plants without 

 soil extract seeding were of very limited development and quite 

 free from nodules. In pots 2 and 3, with soil extract seeding, the 

 root development was very great, and the roots showed several 

 large swellings ; the ends of the roots were thickly covered with 

 root-hairs, probably indicating an effort to acquire wa^ r and 

 mineral nutriment in quantity commensurate with the lirge 

 amount of nitrogen fixed, and so rendered available to the plant. 

 In the garden soil the root development and nodule formation 

 were much less. 



The blue lupins again failed, with the exception of one plant 

 in one pot. The red clover and lucerne are left for further 

 growth. In pot i (unseeded) of the lucerne the plants do 

 not appear to have grown at all since a few weeks after the 

 seeds were sown, and for a long time there seemed to be no 

 increased growth in pots 2 and 3, which were seeded with 

 garden soil extract. Pot 2 had, therefore, a fresh quantity of 

 soil extract — this time from a soil where lucerne was growing — 

 added ; this also seemed for some time to have no effect, but 

 subsequently there was some increased depth of colour and some 

 increased growth. Pot 3 was watered with a dilute solution of 

 calcium nitrate, which soon produced a very marked and bene- 

 ficial effect. With regard to the red clover, the results are, as 

 yet, uncertain ; both in the pots to which soil extract was added, 

 and in that which had no soil extract, there is much more growth 

 than is believed can be accounted for by nitrogen in the seed 

 sown. The glass house in which the experiments are made 

 stands in the middle of allotment gardens where vegetables of 

 all kinds are grown, and this fact, viewed in the light of Hell- 

 riegel and Wilfarth's more recent results, already referred to — 

 according to which the best results with clover are obtained by 

 seeding with organisms from a root-crop soil — points to a pos- 

 sible acquisition of organisms from the air as the most probable 

 explanation. 



Attention is drawn to the widely different external appear- 

 ance of the tubercles of the different plants. In the case of 

 peas, they occurred generally as agglomerations ; on the roots 

 of vetches the nodules were generally single. Lupins seem to 

 have two kinds of tubercular development, the most prevalent 

 being "swellings " which entirely encase the thick roots ; the 

 "nodules" are generally small, and are distributed on the root- 

 fibres. The lucerne nodules are, again, quite different in form 

 from any of those already mentioned, being long, and generally 

 divided or branched. 



Returning to the main object of the investigation, the results 

 confirm those of Hellriegel and Wilfarth, in showing the fixa- 

 tion of free nitrogen under the influence of microbe-seeding of 

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

 ■case of the leguminous plant. . 



It appears that, concurrently with the experiments mide at 

 Rothamsted, M. Breal, of the Museum d'Histoire Naturelle of 

 Paris, has made various experiments instigated by the results 

 of Hellriegel and Wilfarth, and his results also confirm those of 

 Hellriegel. 



Hellriegel agrees with the authors that the LegmninoscE utilize 



soil nitrogen. He considers that the soil would be drawn upon 

 first, and that this source is supplemented by the elementary 

 nitrogen of the air, brought into combination by means of the 

 organisms ; he also considers that there would be more or less 

 fixation even with a soil rich in nitrogen. On the other hand, 

 Vines found the formation of tubercles, and presumably also the 

 fixation of free nitrogen, is much reduced, or even stopped alto- 

 gether, by the application of much nitrate to the soil ; and the 

 Rothamsted experiments indicate, that with a rich garden soil 

 there are far fewer nodules formed, than with a sand contain- 

 ing but little nitrogen, and seeded with soil organisms. If 

 subsequent experiments should show this to be the case, the 

 amount of nitrogen of a crop, derived from the air, and the 

 amount derived from a soil, would vary very much according to 

 circumstances ; fixation would take place most freely in the case 

 of a sandy, or poor and porous soil, and less in a richer soil. 



Upon the whole, it is considered that the evidence at com- 

 mand points to the conclusion that, in the case of most, if not 

 all our leguminous crops, more or less of their nitrogen will be 

 due to fixation under the conditions supposed. 



Regarding the mode in which the organisms, which, in sym- 

 biosis with the higher plants, bring about the fixation, although 

 Marshall Ward, Prazmowski, and Beyerinck have already con- 

 tributed interesting results as to the mode of life of these bodies, 

 much has yet to be learnt on the subject before an adequate 

 explanation of the phenomena involved can be given. The 

 authors suggest the following alternatives : — "(i) That, some- 

 how or other, the plant itself is enabled, under the conditions 

 of symbiotic life, to fix free nitrogen of the atmosphere by its 

 leaves — a supposition in favour of which there seems to be no 

 evidence whatever. (2) That the parasite utilizes and fixes free 

 nitrogen, and that the nitrogenous compounds formed are taken 

 up by the host. On such a supposition, the actually ascertained 

 large gain of nitrogen by the leguminous plant growing in a 

 nitrogen-free, but properly infected soil, becomes intelligible." 



In their former paper {loc. cit.) the authors had stated tlT-t 

 all the evidence that had been acquired in lines of inquiry pic- 

 viously followed had failed to solve conclusively the question of 

 the sources of the whole of the nitrogen of the Lcgiiminosm, 

 and that hence it should not excite surprise that new light should 

 come from a new line of inquiry. 



" The question suggests itself, whether such, or allied agency, 

 comes into play in the nitrogen assimilation of leguminous plants 

 generally, or that of other than the agricultural representatives 

 of the non-leguminous families to which we owe such plants, or 

 of those of the numerous and varied other families of the veget- 

 able kingdom. 



" It is true that the families which contribute staple agricul- 

 tural plants are but few, and that the agricultural representatives 

 of those families are also comparatively few. The families so 

 contributing are, however, among the most important and widely 

 distributed in the vegetable kingdom ; as also are some of the 

 plants they contribute. As prominent examples may be men- 

 tioned the Graminea:, affording the cereal grains, a large pro- 

 portion of the mixed herbage of grass-land, and other products ; 

 also the Leguminosa:, yielding pulse-crops, many useful herbage 

 plants, and numerous other products. As we have said, there 

 does not seem to be an unsolved problem as to the sources of 

 the nitrogen of other of our agricultural plants than those 

 of the leguminous family. Obviously, however, it would be 

 unsafe to generalize in regard to individual families as a whole, 

 from results relating to a limited number of examples supplied 

 by their agricultural representatives alone. Still, there is nothing 

 in the evidence at present at command to point to the supposi- 

 tion that there is any fundamental difference in the source of 

 the nitrogen of different members of the same family, such as is 

 clearly indicated between the representatives of the leguminous, 

 and of the other families, supplying staple agricuhural products. 

 On the other hand, existing evidence does not afford any means 

 of judging whether or not similar, or allied agencies to those 

 now under consideration, or even quite different ones, may come 

 into play in the nitrogen assimilation of other families which 

 contribute such a vast variety of vegetation to the earth's 

 surface." N. H. J. M. 



UNIVERSITY AND EDUCATIONAL 



INTELLIGENCE. 



Cambridge. — At the meeting of the Philosophical Society, 



on Monday, May 12, at 4.30 p.m., the following papers are 



promised : — 



