530 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
contained in the seed sown is supplied. We have made a series of experiments, in which 
such growth was attained by means of a supply of combined Nitrogen beyond that con- 
tained in the seed. It remains to see whether, under these conditions of growth, the 
assimilation of free Nitrogen can take place, and thus the above paradox be obviated 
by the proof that the last of the three suppositions is incorrect. 
It is true that we have pointed out the improbability of an assimilation of free Nitro- 
gen in the presence of an excess of combined Nitrogen only so far as the vital process 
of the vegetable cell is concerned. In that intermediate process by which oxygen is 
taken up and carbonic acid formed in the cell, the results due to an excess of com- 
bined Nitrogen might be different. 
Thus, the more active the growth, the greater must be the amount of newly-formed 
carbon-matter capable of consuming oxygen, when the plant is removed from the 
influence of sunlight into the dark. That is to say, the more vigorous the growth in 
the sunlight, the greater might be the reducing power of the plant in the dark. The 
greater the reducing power of the plant, the more nearly will the tendency of its mole- 
cular forces approximate to an evolution of hydrogen which, in the presence of free 
Nitrogen dissolved in the fluids of the cell, may tend to form ammoniacal compounds, 
to be, on the return of light, appropriated by the plant in the exercise of its growing 
functions. In connexion with this point, it may be here mentioned that in our investi- 
gation of the gases given off by plants under different circumstances, we have had an 
evolution of oxygen one day as a coincident of growth, and an evolution of hydrogen 
the next as the result of decomposition. 
Our experiments in which the plants have been manured with limited amounts of 
combined Nitrogen will not only enable us to meet some of the questions above 
suggested, but they will also prove whether or not the conditions of soil, atmosphere, 
temperature, &c., to which our experimental plants have been subjected were consistent 
with active and vigorous growth. 
The fact of the evolution of Nitrogen in the decomposition of nitrogenous organic 
matter, illustrated in Sub-section D, p. 497 et seg., indicated the danger of using such 
matter as a source of supply of Nitrogen. We have therefore used solutions of sul- 
phate of ammonia (see Appendix, p. 542), by means of which we have been enabled to 
supply the plants with known quantities of combined Nitrogen at pleasure, as the pro- 
gress of growth seemed to require. 
In the following Table (XIV.) are given the numerical results of the.experiments on 
the question of the assimilation of free Nitrogen in which the plants were supplied with 
combined Nitrogen beyond that contained in the seed sown. See also figs. 7, 8, 9, 10, 
11, and 12, Plate XV., showing the character and extent of growth of six Graminaceous 
plants with extraneous supply of combined Nitrogen, corresponding to the six above 
them without such supply. 
