70 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT ON THE 
It will be,seen that the results are not only confirmatory of those given by 
Helleiegel the year before, but that they are even much more definite and striking. 
Thus, taking no account of the fraction of a milligram of combined nitrogen supplied 
in the soil-extract, the amount of dry matter produced is nearly 50 times, and the 
amount of nitrogen assimilated is nearly 100 times, as much with, as without, the 
soil-extract! 
The negative result with Graminese, Chenopodiacese, Cruciferse, and Polygoneae, is 
certainly just what would be expected from all that is known of the influence of soil- 
supplies of nitrogen on the growth of the agricultural representatives of those families. 
It will be observed, however, that whilst with oats and buckwheat as representatives 
of the Gramineae and the Polygoneae, Helleiegel and Wilfaeth got negative 
results, it was chiefly with rye-grass and buckwheat that M. JouLiE obtained such 
great gains, though it is true under very different conditions as to soil-supphes of 
nitrogen, whilst some of his greater gains were largely in the soil as well as in the 
plants. 
But whilst experience, whether practical or experimental, does not point to an 
unsolved problem in the matter of the sources of the nitrogen of the agricultural 
pknts of the families above enumerated, it is far otherwise so far as the Papilionacese 
are eoncerned. It is true that, besides other evidence, our own results, recorded in 
this and former papers, show that even these plants do avail themselves of nitrogen 
existing as nitrates within the soil ; and Helleiegel also distinctly recognises that 
such is the ease. At the same time, in reference to our own experiments we have 
admitted that the evidence adduced does not justify the conclusion that nitrates 
within the soil were an adequate source of the whole of the nitrogen that was taken 
up in some of the cases cited. Indeed, although the question of the sources of the 
nitrogen of the Leguminosse has been the subject of experiment and of controversy 
for about half a century, it is generally admitted that all the evidence that has been 
acquired on lines of inquiry until recently followed have failed to solve the problem 
conclusively. It should not, therefore, excite surprise that any new light should 
come from a new line of inquiry. Hence should be recognised, whether as real 
advance in knowledge, or as only incentive to further investigation, the importance of 
the cumulative evidence of the last few years—of which that furnished by the experi¬ 
ments of Helleiegel and Wilfaeth is certainly the most deflnite and the most 
striking, pointing to the conclusion that although chlorophyllous plants may not 
directly utilise the free nitrogen of the air, some of them, at any rate, may acquire 
nitrogen brought into combination under the influence of lower organisms, the 
development of which is, apparently, in some cases a coincident of the growth of the 
higher plant whose nutrition they are to serve. 
Such a conclusion is, however, of such fundamental, and of such far-reaching 
importance, that further proof must yet be demanded, before it can be acce[)ted as 
beyond question. Should it be eventuall}^ established, it would certainly suffice 
