November 12, 1891] 



NATURE 



for some other plants from soil where the particular plant 

 was growing. In all, in 1889 and subsequently, they had 

 grown in this way four descriptions of annual plants 

 — namely, peas, beans, vetches, and yellow lupins ; and 

 four descriptions of longer life — namely, white clover, 

 red clover, sainfoin, and lucerne. Enlarged photographs 

 of the above ground-growth, and of the roots, of the peas, 

 the vetches, and the lupins, so grown, were exhibited. 

 Without microbe-seeding there was neither nodule- 

 formation nor any gain of nitrogen ; but with microbe- 

 seeding there was nodule-formation, and, coincidently, 

 considerable gain of nitrogen. 



As, however, in this exact quantitative series, the 

 plants were not taken up until they were nearly ripe, it 

 was obvious that the roots and their nodules could not 

 be examined during growth, but only at the conclusion, 

 when it was to be supposed that the contents of the 

 nodules would be to a great extent exhausted. Another 

 series was, therefore, undertaken, in which the same four 

 annuals, and the same four plants of longer life, were 

 grown in specially made pits, so arranged that some of 

 the plants of each description could be taken up, and 

 their roots and nodules studied, at successive periods of 

 growth : the annuals at three periods — namely, first when 

 active vegetation was well established, secondly when it 

 was supposed that the point of maximum accumulation 

 had been approximately reached, and thirdly when nearly 

 ripe ; and the plants of longer life at four periods— 

 namely, at the end of the first year, and in the second 

 year when active vegetation was re-established, when the 

 point of maximum accumulation had been reached, and 

 lastly when the seed was nearly ripe. Each of the eight 

 descriptions of plant was grown in sand (with the plant- 

 ash), watered with the extract from a rich soil ; also in a 

 mixture of two parts rich garden soil and one part of 

 sand. In the sand the infection was comparatively local 

 and limited, but some of the nodules developed to a great 

 size on the roots of the weak plants so grown. In the 

 rich soil the infection was much more general over the 

 whole area of the roots, the nodules were much more 

 numerous, but generally very much smaller. Eventually 

 the nodules were picked off the roots, counted, weighed, 

 and the dry substance and the nitrogen in them deter- 

 mined. 



Taking the peas as typical of the annuals, and the 

 sainfoin of the plants of longer life, the general result 

 was, that at the third period of growth of the peas in 

 sand the amount of dry matter of the nodules was very 

 much diminished, the percentage of nitrogen in the dry 

 matter was very much reduced, and the actual quantity 

 of nitrogen remaining in the total nodules was also very 

 much reduced. In fact the nitrogen of the nodules was 

 almost exhausted. The peas grown in rich soil, however, 

 maintained much more vegetative activity at the con- 

 clusion, and showed a very great increase in the number 

 of nodules from the first to the third period ; and with 

 this there was also much more dry substance, and even 

 a greater actual quantity of nitrogen, in the total nodules 

 at the conclusion. Still, as in the peas grown in sand, 

 the percentage of nitrogen in the dry substance of the 

 nodules was very much reduced at the conclusion. In 

 the case of the plant of longer life, the sainfoin, there was, 

 both in sand and in soil, very great increase in the num- 

 ber of nodules, and in the actual amount of dry substance 

 and of nitrogen in them, as the growth progressed. The 

 percentage of nitrogen in the dry substance of the nodules 

 also showed, even in the sand, comparatively little reduc- 

 tion, and in soil even an increase. In fact, separate 

 analyses of nodules of different character, or in different 

 conditions, showed that whilst some were more or less 

 exhausted and contained a less percentage of nitrogen, 

 others contained a high percentage, and were doubtless 

 new and active. Thus, the results pointed to the inter- 

 esting conclusion, that, in the case of the annual, when 



NO. 1150, VOL. 45] 



the seed is formed, and the plant more or less exhausted, 

 both the actual amount of nitrogen in the nodules, and its 

 percentage in the dry substance, are greatly reduced, but 

 that, with the plant of longer life, although the earlier 

 formed nodules become exhausted, others are constantly 

 produced, thus providing for future growth. 



As to the explanation of the fixation of free nitrogen, 

 the facts at command did not favour the conclusion that 

 under the influence of the symbiosis the higher plant 

 itself was enabled to fix the free nitrogen of the air by 

 its leaves. Nor did the evidence point to the conclusion 

 that the nodule-bacteria became distributed through the 

 soil and there fixed free nitrogen, the compounds of 

 nitrogen so produced being taken up by the higher 

 plant. It seemed more consistent, both with experimental 

 results and with general ideas, to suppose that the nodule- 

 bacteria fixed free nitrogen within the plant, and that the 

 higher plant absorbed the nitrogenous compounds pro- 

 duced. In other words, there was no evidence that the 

 chlorophyllous plant itself fixed free nitrogen, or that the 

 fixation takes place within the soil, but it was more prob- 

 able that the lower organisms fix the free nitrogen. If 

 this should eventually be established, we have to re- 

 cognize a new power of living organisms — that of as- 

 similating an elementary substance. But this would only 

 be an extension of the fact that lower organisms are 

 capable of performing assimilation-work which the 

 higher cannot accomplish ; whilst it would be a further 

 instance of lower organisms serving the higher. Finally, 

 it may here be observed that Loew has suggested that the 

 vegetable cell, with its active protoplasm, if in an alkaline 

 condition, might fix free nitrogen, with the formation of 

 ammonium nitrite. Without passing any judgment on 

 this point, it may be stated that it has frequently been 

 found at Rothamsted that the contents of the nodules 

 have a weak alkaline reaction when in apparently an 

 active condition— that is, whilst still flesh-red and 

 glistening. 



As to the importance of the fixation for agriculture, 

 and for vegetation gfenerally, there is also much yet to 

 learn. It is obvious that different Papilionaceae growing 

 under the same external conditions manifest very dif- 

 ferent susceptibility to, or power to take advantage of, the 

 symbiosis. The fact, as shown by Prof. Nobbe, that 

 Papilionaceous shrubs and trees, as well as herbaceous 

 plants, are susceptible to the symbiosis, and under its in- 

 fluence may gain much nitrogen, is of interest from a 

 scientific point of view as serving to explain the source of 

 some of the combined nitrogen accumulated through ages 

 on the surface of the globe ; and also from a practical 

 point of view, since, especially in tropical countries, such 

 plants yield many important food materials, as well as 

 other industrial products. 



In conclusion, it will be seen that the experimental 

 results which have been brought forward constitute only 

 a small proportion of those already obtained or yet to be 

 obtained at Rothamsted, but they have been selected as 

 being to a great extent typical, and illustrative of the 

 lines of investigation which are being carried out. 



FOSSIL BIRDS IN THE BRITISH MUSEUM} 



IT is always a matter of extreme interest to trace back 

 any group of beings to their first recorded appearance 

 in geological history, and the task becomes the more 

 attractive in proportion to the rarity of the organism 

 sought for. 



The fossil remains of birds, which form the subject of 

 Mr. Lydekker's Catalogue, constitute nearly the smallest 



' " Catalogue of the Fossil Birds in the British Museum (Natural 

 History), Cromwell Road, S.W." By Richard Lydekker, B.A., F.G.S., 

 F.Z.S. Pp. xxviii. and 368. (London: Printed by Order of the 

 Trustees. Longmans and Co. ; B. Quaritch ; Asher and Co. ; Kegan Paul 

 and Co., 1R91.) 



