582 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
As in the case of the experiments already considered, so again with those to which 
the Table just given relates, it is seen, by reference to the last column, that there was a 
slight gain of Nitrogen in the experiments of 1857, but, almost without exception, a loss 
rather than a gain in those of 1858. Considering that there was a possible source of 
gain in 1857 in connexion with the slates used in that year (as explained below), and 
with the results of 1858 showing generally a loss rather than a gain when slates were 
not employed, we can interpret the whole in but one way. 
In order to bring out fully the evidence afforded by these results of experiments in 
which the plants were supplied with more or less of combined Nitrogen during the pro- 
gress of growth, we must consider them in three separate aspects :— 
1. As regards the actual gain or loss of Nitrogen, as indicated by the figures given in 
the last column of the Table (XIV.). 
2. As presented in the physiological evidence afforded during growth. 
3. As exhibited on comparison with the experiments in which the plants had no other 
supply of combined Nitrogen than that of the original seed. 
1. The Numerical Results of Table XIV. 
Much that has been said with respect to the plants grown without extraneous supply 
of combined Nitrogen applies with equal force to those now under consideration ; and, 
so far as the evidence relating to the latter is of a different character, owing to the 
amount of combined Nitrogen at the disposal of the plants, it still is no more indicative 
of an assimilation of free Nitrogen than was that obtained with the plants grown with- 
out any artificial supply of combined Nitrogen. 
In illustration of the probability that the slates used as lute-vessels were a source of 
Nitrogen to the plants grown in 1857, some of the observations made during growth 
should be adverted to. It is seen that the barley grown in pumice (1857) gives the largest 
gain of Nitrogen; and it was observed that, soon after watering with the fluid drawn off 
from the surface of the slate, the pumice became covered with a slight coating of green 
matter. And nearly all the slates were found at the end of the experiment to have a 
slight coating of similar character beneath the pans in which the pots which contained 
the plants stood; whilst, in the experiments of 1858, when glazed earthenware lute- 
vessels were employed, no such phenomenon was observed. 
The slight loss of Nitrogen exhibited in the experiments of 1858 is easily accounted 
for on a consideration of the conditions involved. With regard to the peas, clover, 
and beans, the physiological circumstances of growth detailed in the Appendix, taken 
in connexion with the evidence that has been adduced as to the loss of N itrogen during 
the decomposition of nitrogenous organic matter, must be supposed to explain the loss 
in their case, as in some of the experiments in which no extraneous supply of combined 
Nitrogen was employed. 
The loss of Nitrogen indicated in the cases of the wheat, barley, oats, and buck- 
