The Sources of the Nitrogen of our Leguminous Crops. 685 
from that in pots 2 and 3 with the soil-extract only. The main 
root, at a depth of 2 inclies, threw out many thread-like branches, 
at the end of each of which there was a bundle of fine fibre. 
The lower fibres became thicker, and were white and fleshy ; but 
they were without the marked development of root-hairs ob- 
served in such abundance in pots 2 and 3. Most of the root 
was within 6 inches of the surface, and there seemed to be none 
below 14 inches. One or two inches from the surface there were 
swellings on the main roots, which were less raised, but more 
spreading, than those on the roots in pots 2 and 3. There were 
also, on one side branch, six very small nodules. 
To sum up in regard to the yellow lupins : in the sterilised 
quartz sand, without soil-extract seeding, the growth was ex- 
tremely limited both above and under ground. Under the in- 
fluence of the lupin soil-extract seeding, the above-ground growth 
was not only very luxuriant, but the plants developed considerable 
maturing tendency, flowering and seeding freely. The develop- 
ment of the roots generally, and that of swellings or nodules on 
them, were also very marked. In pot 4, with the lupin-sand 
itself, which would supply a not immaterial amount of combined 
nitrogen, although the growth was fairly normal, it was, both 
above ground and within the soil, much less than in the pots 
with sail-extract only ; and the development of nodules was also 
less. It is probable that the less growth in the lupin-sand itself, 
than in the quartz sand with soil-extract, was largely due to the 
much less porosity of the lupin soil, especially when watered. 
I Again, as with the peas and the vetches, so loith the lupins, 
vnthaut soil-extract seeding, there vjus very limited^ groiuth, no 
■ Jormation of nodides, and no gain of nitrogen ; hut, with soil- 
i extract seeding, there teas luxuriant growth, abundant nodide- 
j formation, and, coincidently, great gain of nitrogen. There was, 
I in fact, very many times as much nitrogen in the products of 
' growth as in the seed sou-n. 
The foregoing results with peas, vetches, and yellow lupins 
are very definite and very striking. They are abundantly illus- 
trative of the fact that under the influence of suitable microbe- 
seeding of the soil, there is nodule-formation on the roots, and, 
coincidently, increased growth, and gain of nitrogen beyond 
that supplied in the soil and in the seed as combined nitrogen, 
presumably due to the fixation, in some way, of free nitrogen.' 
' MM. Schloesing fils and Laurent have shown, by growing Leguminosa^ 
in closed vessels, and the analysis of the air before and after growth, that 
free nitrogen disappeared, in quantity closely corresponding to that gained in 
growth ; thus establishing the fact that the source of the gain was free nitron-en 
{Compt. Rend. cxi. 750). " 
