104 
Drought of 1870 and 
Intimately connected with the greater change in the subsoil 
of the plot manured with nitrate of soda than in that manured 
with ammonia-salts, with the greater predominance and luxuri- 
ance of the deeper-feeding herbage, and with the consequent 
little evil effects from the drought where the nitrate was employed, 
is doubtless the fact that the ammonia of the ammonia-salts is 
much more readily absorbed and retained by the soil than is the 
nitric acid of the nitrate. The latter, consequentl}", becomes, 
under the influence of rain, more rapidly distributed and washed 
into the subsoil, whither the roots follow it. As this filtration, 
into and through the subsoil, of a solution of the nitrate, or of its 
products of decomposition within the soil, has been proceeding 
for thirteen years in succession, there is little cause for surprise 
that the subsoil should have become much more changed than 
where the ammonia-salts had been used. It seems intelligible, 
too, that those plants of the herbage, whose habit of growth is 
characterised by a comparatively large development of descend- 
ing roots, aided as they would be when once they had asserted 
their predominance by more and more self-sowing each succeeding 
year, should get such complete possession of the lower layers of the 
soil, with their stores of food and moisture. On this point it may 
be remarked, that the Bronnis mollis, which so strikingly predomi- 
nated on the nitrated plot, and whose roots, though only a biennial, 
had obtained more complete possession of the subsoil than those 
of any other plant, is one of the earliest of the grasses, and has, in 
point of fact, generally seeded to a greater or less extent before 
the crop has been cut. 
It may be here mentioned in passing, that, wherever, in the 
course of the experiments at Rothamsted, nitrate of soda is 
employed year after year on the same plot of arable land, the 
difference in the appearance and texture of the soil is very great, 
and is discernible at a considerable distance. The soil appa- 
rently retains very much more moisture, becomes more aggluti- 
nated, and so sticky compared vv'ith that of adjoining plots under 
equal conditions of weather, as to be with difficulty worked at 
the same time, and never brought to the same tilth Avithout the 
expenditure of extra labour upon it. It may be judged, indeed, 
that during the wet season the nitrated soil, and its more dis- 
integrated subsoil, would acquire more moisture, or at least more 
available moisture, than the soil and raw clayey subsoil of the 
other plots. 
We have, then, in the properties of the nitrate of soda and its 
effects upon the soil and subsoil, in the influence of these in 
determining the character of the prevailing herbage, and in the 
comparative independence of external sources of moisture which 
a deep root range gives to the plants encouraged, an explanation 
