662 The Sources of the Nitrogen of our Legnminotis Crops. 
paratively low percentage of nitrogen in their dry substance, 
and by yielding comparatively large amounts of the ?ion-nitro- 
genous products — starcb, sugar, and cellulose — are especially 
benefited by the application of nitrogenous manures, and under 
their influence yield greatly increased amounts of those non-nitro- 
genous bodies ; whilst the leguminous crops, which contain a 
much higher percentage of nitrogen, and yield much more 
nitrogen over a given area of land, under the same soil and 
season conditions, are much less benefited by such manures. 
Without attempting to give an adequate physiological ex- 
planation of this curious result, some of the facts bearing upon 
it may be briefly stated as follows : The non-leguminous crops 
having comparatively limited power of accumulating nitrogen 
under given soil conditions, they generally require nitrogenous 
manuring ; the amount of nitrogen assimilated to a great extent 
rules the amount of chlorophyll formed ; chlorophyll formation is 
an essential condition of carbon assimilation ; the amoxmt of 
carbon assimilated is the chief measure of the amount of pro- 
duce ; and since the more special or characteristic products of 
the non-leguminous crops are the non-nitrogenous substances — 
the carbohj'drates, the natural result of the increased assimila- 
tion of nitrogen, and the consequent increased luxuriance, is an 
increased formation of the bodies which are their essential or 
characteristic products. 
The fact is, that whilst it can hardly be said that there remains 
an unsolved problem in the matter of the sources of the nitrogen 
of our Tion-leguminous crops — of wheat, of barley, and of grasses, as 
representatives of the great family of the Graminece ; of turnips, 
representing the Criicifene ; of some varieties of beet, represent- 
ing the Ghenopodiacece ; and of potatoes of the Solanece — it must 
be admitted to be quite otherwise so far as our leguminous crops 
are concerned. 
It is nearly a century ago since the question whether plants 
took up, or evolved, free nitrogen became a matter of" experi- 
ment and of discussion ; and it is just about half a century since 
Boussingault commenced experiments to determine whether 
plants assimilate free nitrogen. From his results he concluded 
that they did not ; and those obtained at Eothanisted about thirty 
years ago confirmed the conclusions of Boussingault. In fact, 
we concluded that under the conditions of those exjieriments, 
which were those of sterilisation and enclosure, in which there- 
fore the action both of electricity and of microbes was excluded, 
the results were conclusive against the supposition that, under 
such conditions, the higher chloropliyllous plants can directly 
fix free nitrogen, either by their leaves or otherwise. 
