680 The Sources of the l^itrogen of our Leguminous Crops, 
portance and of the significance of the results which have so far 
been obtained. 
The peas were sown on July 10, two seeds being put into 
each of the four pots ; and the plants were taken up on October 
23 and 24. Photogi'aphs of the four pots of plants were taken 
on August 3, August 20, September 27, and lastly on October 
22 ; that is, the day before taking up. Unlike the result obtained 
in pot 1 in 1888 with impure and non-sterilised sand, the plants 
of 1889, in the purer and sterilised quartz sand, showed 
extremely limited growth. Before the end of July, those in both 
pots 2 and 0, with soil-extract seeding, began to show enhanced 
growth compared with that in pot 1, without the soil-extract ; 
and, eventually, whilst the plants in pot 1 were only 8J and 8^ 
inches in height, those in pot 2, with soil-extract, were 1-i and 
50i inches ; and those in pot 3, also with soil-extract, were 40;^ 
and 39^^ inches high. In pot 4, with the garden soil, the 
heights of the plants were 38i and 4H inches, or only about 
the same as in pot 3 with the soil-extract only. But the plants 
in pot 4 were more vigorous, and whilst they flowered and seeded, 
neither of those in either pot 2 or pot 3 did so, but continued to 
vegetate, the upper parts apparently at the expense of the lower. 
Then as to the root development : — In pot 1, without soil- 
extract, and with extremely limited above-ground growth, it 
was altogether much less than in either pot 2 or pot 3 with 
soil-extract, or than in pot 4 with garden soil. Again, in pot 1, 
without soil-extract seeding, the main roots descended some 
distance before they threw out any considerable amount of root- 
branches and root-fibre ; whereas, in pots 2 and 3, with soil- 
extract, there was characteristically much more fibre distributed, 
both in the upper layers and throughout the pot. 
It is specially to be noted that, whereas in pot 1 in 18SS, 
with impure and non-sterilised sand, there was some development 
of nodules, now, in the pure and sterilised sand, not a nodule was 
observable. 
In pot 2, with soil-extract seeding, one plant was very much 
larger than the other, and developed much more root. The 
smaller plant had, however, several nodules on the main root, 
near the surface of the soil, and a good many small ones distri- 
buted along the fibres. Most of the nodules were more or less 
shrivelled. The larger plant had a large cluster of nodules on 
the main root, very near the surface ; and a very large number 
of single nodules, mostly small, was distributed on the root-fibres, 
quite to the bottom of the pot. Upon the whole those on the 
larger plant were less shrivelled. 
