The Sources of the Nitrogen of ovr Legiminous Crops. 667 
entered the glass shade, from which it passed, by the exit tube, 
through an eight-bulbed apparatus containing sulphuric acid, by 
which communication with the unwashed external air was pre- 
vented. Carbonic acid was supplied as required by adding a 
measured quantity of hydrochloric acid to a bottle containing 
fragments of marble, the evolved gas passing through one of the 
bottles of sulphuric acid, through the long tube, and through the 
carbonate of soda solution, before entering the shade. 
In 1857 twelve sets of such apparatus were employed; in 
1858 a larger number, some with larger lute- vessels and shades ; 
I in 1859 six, and in 18G0 also six. Each year the whole were 
I arranged side by side, on stands of brickwork ; in the open air. 
I The numerical results obtained in the experiments of 1857 and 
I 1858 are summarised in Table II. (p. 668). 
I The upper part of this Table shows the results obtained 
i in 1857 and 1858. in the experiments in which no combined 
nitrogen was supplied beyond that contained in the seed sown. 
The growth was extremely restricted under these conditions, and 
the figures in the table show that, neither with the Gh-aminece, 
the Leguminosce., nor the Polygonacece (buckwheat), was there in 
any case a gain of three milligrams of nitrogen. In most cases 
there was much less gain than this, or a slight loss. There was, in 
fact, nothing in the results to lead to the conclusion that either of 
these different descriptions of plant had assimilated free nitrogen. 
The lower part of the Table shows the results obtained in the 
experiments in which the plants were supplied with known 
quantities of combined nitrogen, in the form of a solution of 
ammonium-sulphate, applied to the soil. The effect of this 
direct supply of combined nitrogen was to increase the growth 
in a very mai'ked degree, especially in the case of the Graminece. 
The figures in the table show that the actual gains or losses of 
nitrogen ranged a little higher in these experiments, in which 
larger quantities were involved ; but they are always represented 
by units of milligrams only, and the losses are higher than the 
gains. Further, the gains, such as they are, are all in the experi- 
ments with the Graminece, whilst there is in each case a loss with 
the Leguminoso', and with the buckwheat. The losses, if beyond 
the limits that might be expected from experimental error, are 
doubtless due to decay of organic matter, fallen leaves, &c. 
It should be stated that the growth was far more healthy with 
the Graminece than with the Leguminosce, which are, even in the 
open field, very susceptible to vicissitudes of heat and moisture, 
and were found to be extremely so under the conditions of enclo- 
sure under glass shades. It might be objected, therefore, that 
the negative results with the Leguminosce are not so conclusive 
