686 The Sources of the Nitrogen of our Leguminous Crops.^ 
As already said, experiments were also made with a fourth 
annual, namely beans ; and with four plants of longer life — 
white clover, red clover, sainfoin, and lucerne. With some of 
these the growth was not so satisfactoiy as with the peas, the 
vetches, and the yellow lupins ; partly owing to failure to 
ensure suitable infection of the I'oots. With both clovers there 
will doubtless be considerable gain, especially with the white 
clover, which, however, is still growing. 
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 Rothamsted with both 
blue and yellow lupins in 1888, and with blue lupins in 1889, 
was doubtless mainly 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.^ He undertook an investigation, 
in the first place to determine whether leguminous trees, as well 
as our agricultural leguminous plants, were susceptible to 
microbe infection and nodule-formation ; and secondly 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, Fohinia ji^tudacdcia (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 residts were somewhat irregular. For example, with 
peas a better result was obtained by the use of Gleditschia, 
Robinia, or Cytisus, soil-extract, than of pea soil-extract;. With 
liohinia, on the other hand, the best result was obtained with 
Rohinia soil-extract. 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. 
Thus, with peas there was more produce, and more nitrogen 
assimilated, by the application of pure cultivations of pea nodule 
and pea soil bacteria, than by that of lupin nodule, lupin soil, 
' Vermehe iiher die Sticlistoff-Assimilation der Legumi)wsen. F. Nobbe, 
E. Schmid, L. Hiltner, E. Hotter. Versuchs-Stationen, xxxix. 327. 
