150 



THE ROTHAMSTED EXPERIMENTS. 



Microbe- 

 infection 

 and nod- 

 ule forma- 

 tion. 

 JVobbe's 

 inquiry. 



cuttings, and was not taken up until the winter of 1890-91. 

 Pot 1, without soil-extract seeding, obviously became acci- 

 dentally microbe-seeded ; the growth was considerable, there 

 were nodules on the roots, and there was considerable gain. 

 There was also much nodule-formation, and there was great 

 gain of nitrogen, under the influence of the soil- extract 

 seeding, but less than in the case of the white clover. 



The sainfoin was sown in June 1890, and the growth was 

 very limited — supposed to be accounted for by imperfect 

 microbe-infection of the roots — and the gain was accordingly 

 but small. 



The lucerne grew much better than the sainfoin ; the roots 

 were much more infected by the microbe-seeding, and there 

 was accordingly considerable gain of nitrogen. 



In reference to the failure of growth in the cases where it 

 was apparently due to failure to obtain suitable microbe- 

 infection, it has already been said that Hellriegel at first 

 found great difficulty in ensuring a good result with lupins, 

 serradella, and some other plants, among which was red 

 clover ; and the failure to obtain good results at Eothamsted 

 with both blue and yellow lupins in 1888, and with blue 

 lupins in 1889, was doubtless partly due to the same cause. 



As bearing upon this curious and interesting point, it will 

 be well briefly to refer here to the experiments and results 

 of Professor Nobbe on this subject. 1 He undertook an in- 

 vestigation to determine whether leguminous trees, as well 

 as our agricultural leguminous plants, were susceptible to 

 microbe-infection and nodule-formation; and also to ascer- 

 tain whether there is one nodule - forming bacterium, or 

 whether many bacteria have the property — each description 

 of plant, or perhaps each group, having its special bacterium. 



The plants he experimented upon were peas, yellow lupins, 

 and beans ; also as trees Robinia pseudacacia (locust-tree), 

 Cytisus laburnum (laburnum), and Gleditschia triacantha 

 (honey locust). To each of these he applied microbe-seeding 

 from various sources ; in some cases only soil-extracts, and 

 in others pure cultivations, either from soil-extracts or from 

 the root-nodules of different plants. When soil-extracts only 

 were used, the results were somewhat irregular. But when 

 pure cultivations were employed, the general result was that 

 more effect was produced on any particular description of 

 plant by the bacteria obtained from the same description 

 than by those derived from other descriptions. Nobbe con- 

 cluded that the results can leave no doubt that the pea and 

 the Robinia bacteria have different physiological actions ; 



1 Versuche uber die Stickstoff- Assimilation der Zeguminosen. F. Nobbe, 

 E. Schmid, L. Hiltner, E. Hotter, Versuchs-Stationen, xxxix. 327. 



