580 ME. J. B. LAWES, DB, GILBERT, 1KB DB. PTJGB OH 



contained in the seed sown is supplied. We have made a leries of experiments, in which 

 such growth was attained bj means of a supply of combined Nitrogen beyond thai con- 

 tained in the seed. It remains to sec whether, under these conditions of growth, the 

 assimilation of free Nitrogen can take place, and thus the above paradox be obviated 

 by the proof thai 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 onlj so far as the vital pn 

 of the vegetable cell is concerned. In that intermediate proce by which oxygen if 

 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 \\<i- 

 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 etseq., 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 suppbed with 

 combined Nitrogen beyond that contained in the seed sown. See also figs. T, 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. 



