The Sources of the Nitrogen of our Leguminoiis Crops. 673 
colour, they nevertlieless showed both a less number of leaves, 
and considerably less leaf-surface, than the plants in pot 1 with- 
out the soil-extract. A possible explanation of the fact that the 
plants with the soil-extract seeding remained so long in a com- 
paratively backward condition may be that, in the early stages of 
the development of the nodules and their contents, they rely 
largely for their nitrogenous nutriment on the compounds of 
nitrogen already within the plant, and so the development of the 
higher plant itself is retarded. The figures show, however, that 
from this date, the plants in pots 2 and 3, with the soil-extract, 
gradually gained upon those in pot 1 without it, both in number 
of leaves and in leaf-surface ; until, when the plants were takea 
up on December 14, those in pots 2 and 3 showed 540 and 390 
leaveS) against only 382 on those in pot 1 ; and 481 and 434 of 
leaf- surface, against only 267 in pot 1. There is, therefore, clear 
evidence of increased growth under the influence of the soil- 
extract seeding. 
In all the pots the upper portions of the plants obviously 
developed at the expense of the lower, the leaves of which 
gradually lost colour and withered, whilst the stems and leaves 
of the upper portion increased in growth ; those in pots 2, 3, and 
4, continuing to vegetate and to maintain a bright green colour 
to the last, whilst those in pot 1 showed more exhaustion, and 
maintained much less colour. Probably owing to the lateness of 
the season, there was no indication of flowering in any of the pots. 
The four pots of plants were photographed on September 1, 
September 22, October 6, and lastly on November 3, about five 
■weeks before the taking up of the plants. 
As the roots had to be preserved without any loss for analysis, 
the examination of them had to be very carefully conducted, 
and was necessarily more restricted than if examination had 
been the only object. After the above-ground growth had been 
cut off, the pots, with their moist soil and roots, were kept in a 
warm dry place until the examination commenced. The block 
of soil was carefully turned out on to glazed cartridge-paper, 
and notes were at once taken as to the distribution of roots so 
far as it was then apparent. The sand or soil was then removed 
little by little until the roots were left nearly bare. Further 
notes were then taken, after which the remaining sand or soil 
was removed as far as possible by washing in a beaker with a 
little distilled water. The roots were then mounted upon paper, 
and so photographed, and finally noted upon. 
In order to stimulate and assist the observation of others, it 
will be well to give some description of the development of the 
roots, and of the nodules on them, of the various experimental 
VOL. II. T. S.— 8 Y Y 
