354 Ward —Recent Publications bearing on the 
Lawes and Gilbert give a resume of the question of the 
sources of nitrogen in plants, and especially of their further 
results. In their earlier paper they concluded that, except 
the small annual increment of combined nitrogen washed 
down by rain, the source of nitrogen was substantially the 
stores in the soil. The compared growth of gramineous 
crops and of leguminous crops under parallel conditions 
resulted in the conclusion that more nitric acid accumulated 
in soils under Leguminosae, indicating increased nitrification. 
Attempts to explain the increase of nitrogen under Legu- 
minosae as due to the subsoil, or to the action of acids 
in the roots, &c., failed. 
References are then made to the experiments of Berthelot 
and Andre, and of Loges, showing that the insoluble nitro- 
genous substances in soils are of the nature of amides. 
Experiments are then adduced showing that green plants 
can take up soluble complex nitrogenous organic bodies in 
water-cultures, and possibly they can take up amides in 
the soil. 
Frank’s researches on Mycorhiza are then referred to : 
of course only the earlier paper is quoted. Then comes 
in the question of the participation of free atmospheric 
nitrogen, and the authors reserve their opinion, pointing 
out, however, that the soil contains enormous quantities of 
combined nitrogen, and that there is c obviously still a wide 
field for enquiry as to whether or not, or in what way, the 
very large store of already existing combined nitrogen may 
become available to growing vegetation.’ 
In the above citations it is not by any means to be implied 
that a complete survey of the literature has been given or 
attempted ; several papers have been passed over as either 
generally known, or too technical for the present purpose, 
and of course there is still much discussion on many points — 
e. g. as to the modus operandi of nitrifying organisms 1 , as 
1 See Sehloesing and Muntz in Comptes Rendus, 1879; Warington, Chemical 
Soc. Journal, 1879 onwards; and Berthelot, Comptes Rend. 1876 onwards. 
