353 
Sources of Nitrogen in Plants. 
I now pass to a summary of several other papers re- 
cently published, and bearing on the general question : they 
must, of course, stand on their own merits. In 1885 Ber- 
thelot 1 showed that the amount of combined nitrogen 
in pots of soil, exposed for some months to the atmo- 
sphere, continually increased ; this was proved to be due 
to the absorption and ‘fixation’ of free nitrogen, and much 
in excess of any nitrogen compounds that could be supplied 
in rain, &c. Berthelot showed also that this action does not 
occur if the soil is sterilised by heat, and concludes thence 
that the action is due to the intervention of living organisms. 
The process, moreover, comes to a standstill in the winter, and 
is at its best when vegetation is most active. 
The author concluded that in six months more than 26-32 
kilos of nitrogen per hectare would be absorbed in his ex- 
periments. 
In 1886, M. Berthelot 2 published further results, showing 
that nitrogen is continually absorbed from the air, even when 
no plants are being grown in the soil. The amount ab- 
sorbed is in all cases very much greater than the quantity of 
nitrogen existing as ammonia or nitrogen oxides in the air or 
rain. Much of the absorbed nitrogen is converted into nitrates. 
In the Comptes Rend., T. 104, p. 625, Berthelot again 
publishes results on this subject, especially referring to soil 
in which plants are being grown, and finds that less nitrogen 
is fixed than was the case with fallow soils. A further 
paper appears by the same chemist in the same volume, 
showing that, independently of the other processes, ammonia 
is continually being evolved from vegetable soils. This double 
action — fixation of nitrogen on the one hand, and the escape 
of ammonia on the other — has been noted by other observers 
also. 
In the ‘Proceedings of the Royal Society’ for 1 887 3 , Messrs. 
1 Compt. Rend., T. 101, p. 775. 2 Ibid. T. 104, p. 205. 
3 Proc. Roy. Soc., p. 108, ‘ On the present position of the Question of the 
Sources of Nitrogen of Vegetation, with some new results, and preliminary notice 
of new lines of Investigation.’ 
