THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 541 
the range of conditions possibly favourable for the assimilation of free Nitrogen was, 
therefore, more limited. But the results recorded with these plants, so far as they go, 
do not indicate any assimilation of free Nitrogen. Since, however, in practice, Legu- 
minous crops assimilate, from some source, so very much more Nitrogen than Grami- 
naceous ones, under ostensibly equal circumstances of supply of combined Nitrogen, it 
is desirable that the evidence of further experiments with these plants, under conditions 
of more healthy growth, should be obtained.- 
Results obtained with some other plants are in the same sense as those obtained with 
Graminacee and Leguminose, in regard to the question of the assimilation of free 
Nitrogen. 
In view of the evidence afforded of the non-assimilation of free Nitrogen by plants 
under the wide range of circumstances provided in the experiments, it is desirable that 
the several actual or possible sources of combined Nitrogen to plants should be more 
fully investigated, both qualitatively and quantitatively. 
If it be established that the processes of vegetation do not bring free Nitrogen into 
combination, it still remains not very obvious to what actions a large proportion of the 
existing combined Nitrogen may be attributed. 
