688 The Sources of the Nitrogen of our Leguminoxis Crops, 
of the plants grown at Rothamsted in 1889, whicli have shown 
that the external appearance, and the distribution, of the root- 
nodules were very different in the case of the peas, the vetches, 
and the lupins. In that of the peas there were many of what 
may be called agglomerations of nodules, and comparatively few 
single ones distributed on the root-fibres. On the roots of the 
vetches there were comparatively few agglomerations or bunches, 
and more single nodules, pretty widely distributed along the 
root-fibres. The lupin roots, on the other hand, showed tuber- 
cular developments very different from those on either the pea 
or the vetch roots. Indeed, at the period of examination — that 
is, when the plants were nearly ripe — two apparently distinct 
kinds were observed, one of which, the most prevalent, has been 
spoken of as " swellings," and the other as " nodules." The 
" swellings " were chiefly on the main roots or the thicker 
branches ; where they grew they encased the root entirely, and 
they had a shining and presumably impervious skin. The 
" nodules," on the other hand, were chiefly single, small, and 
distributed on the root-fibres. 
Assuming that the so-called " swellings " (with their con- 
tents) on the roots of the lupins were the bodies which had 
exercised the functions of the " nodules " found on the roots of 
the other plants, it is to be concluded that, after the very luxu- 
riant growth, and the flowering and seeding, their function was 
so far at an end, and they had become suberised. The other 
bodies on the lupin roots, distinguished in the detailed descrip- 
tion as " nodules," indicated too meagre development to have 
had much share in the gi'eat amount of assimilation that had 
been accomplished. On the other hand, the " swellings," which, 
as has been said, were all on the main roots or thicker branches, 
were certainly very characteristic of the roots of the lupin plants 
which attained the greatest growth ; and, assuming that they, 
with their contents, were really the effective bodies, it must be 
supposed that they had been formed where they were found 
whilst the root was still young, and had grown with its growth. 
In favour of this supposition is the fact that the increased 
growth from the soil-extract seeding commenced quite early in 
the life of tlie plants. 
The nodules on the I'oots of lucerne growiug in the field 
were observed at diflerent periods of the season in 1887, and 
again quite recently on plants taken from the field for that 
purpose. They are quite different in general external character 
from those on any of the other plants that have been examined 
at Rothamsted. Instead of being more or less rounded,. they 
have more the appearance of shoots or buds, much longer 
