A great part of this paper was written in the spring of 1886, but its completion was unavoidably delayed. This has, however, not been altogether without advantage. Thus, in the first place, at the
Naturforscher-Versammlung
, held in Berlin, in September, 1886, the greater part of the sittings of two days was devoted, in the Section of
Landwirthschaftliches Versuchs- Wesen
, to the discussion of the subject from various points of view, one of ourselves taking part; and as it seemed desirable that the results and conclusions then brought forward by others should be considered, we have waited for the publication of the exact figures in some cases. Again, since the Berlin meeting, M. Berthelot has published some further results, to which reference should be made. And lastly, we are now enabled to give further new results of our own. In Part 2 of the ‘Philosophical Transactions’ for 1861, a paper was given, by ourselves and the late Dr. Pugh, “
On the Sources of the Nitrogen of Vegetation, with special reference to the question whether plants assimilate free or uncombined Nitrogen
.” Since that time, the question of the sources of the nitrogen of vegetation has continued to be the subject of much discussion, and also of much experimental enquiry, both at Rothamsted and elsewhere. Until quite recently, the controversy has chiefly been as to whether plants directly assimilate the free nitrogen of the atmosphere; but, during the last few years, the discussion has assumed a somewhat different aspect. The question still is whether the free nitrogen of the air is an important source of the nitrogen of vegetation; but whilst few now adhere to the view that the higher chlorophyllous plants directly assimilate free nitrogen, it is, nevertheless, assumed to be brought under contribution in various ways—coming into combination within the soil, under the influence of electricity, or of micro-organisms, or of other low forms, and so indirectly serving as an important source of the nitrogen of plants of a higher order. Several of the more important of the investigations in the lines here indicated seem to have been instigated by the assumption that compensation must be found for the losses of combined nitrogen which the soil sustains by the removal of crops, and also for the losses which result from the liberation of nitrogen from its combinations under various circumstances.
Preface - The British contribution to the SCOPE Programme on the Ecology of Biological Invasions
