The Sources of the Nitrogen of our Leguminous Crops. 679 
about six inclies in diameter, and fifteen inches deep inside ; 
that is, about twice as deep as those used in 1888, and again 
in 1889 and 1890, for the peas, vetches, beans, white clover, and 
red clover. These larger pots had holes at the bottom for 
drainage, and slits at the sides, near the bottom, for aeration. 
Each of the pots, large or small, stood in a specially-made pan 
of the same material. A quantity of broken, washed, and tliis 
time ignited flint was put into the bottom of eacli pot. The sand 
used was a rather coarse white quartz sand, from which the 
coarser and the finer portions were removed by sifting, and more 
of the finer by washing and decantation, first with well, and 
afterwards with distilled, water. In defect of means for igniting 
80 large a quantity of material (several hundred pounds in all), 
without running the risk of gaining more impurity than was 
expelled, the portion retained for use was kept, in successive 
lots, in a large water-bath, at nearly 100° C, for several days, 
and then preserved in well-closed bottles. The results have 
shown that the sand so prepared was sufficiently, if not abso- 
lutely, sterilised. 
In all the experiments commenced subsequently to 1888 
the sand was mixed with only O'l per cent, of the plant ash and 
0"1 per cent, of calcium carbonate. 
There were four pots of each description of plant, excepting 
in the case of the white clover, of which there were five. For 
the peas, vetches, beans, white clover, red clover, sainfoin, and 
lucerne, No. 1 was with the prepared quartz sand, without soil- 
extract ; Nos. 2 and 3 were with the quartz sand and garden soil- 
extract added ; and No. 4 was with the garden soil itself ; the 
fifth pot of white clover receiving calcium nitrate instead of 
soil-extract. Of the lupins (both blue and yellow), No. 1 was 
with the prepared quartz sand, without soil-extract ; Nos. 2 and 3 
were with lupin soil-extract added ; and No. 4 was with the lupin 
sandy soil itself, to which O'Ol per cent, of the plant ash was 
added. 
The soil-extracts were added the day before the sowing of 
the seed; 25 c.c. in the case of the plants grown in the smaller, 
and 50 c.c. in that of those grown in the larger, pots. 
The seeds were selected and weighed as in 1888. 
The analytical details relating to the experiments com- 
menced in 1889, and subsequently, are not yet completed; nor 
have those already available yet been arranged and published, so 
that numerical results cannot be given here. The following 
notes on growth and descriptions of the plants and their roots, 
together with a general statement of the bearing of the analytical 
data in some cases, will, however, convey a clear idea of the im- 
