elds gradually to the atmosphere,
under the action of the powerful evaporation constantly going on, a
large amount of nitrogen in this form. The sources of the nitrogen of
the ocean are the nitrates which it receives from the drainage of land,
animal and vegetable matter, sewage, &c.

[68] See Appendix, Note I., p. 155.

[69] To illustrate this point, it may be mentioned that on the least
windy of days, when the wind is only moving at the rate of two miles an
hour--and this, it may he added, is so slow as to be scarcely
noticeable--the air in a space of 20 feet is changed over five hundred
times in an hour. The combined nitrogen thus absorbed is probably
entirely in the form of ammonia. It would seem so at any rate, from some
experiments by Schloesing. See p. 132.

[70] No vegetable or animal cell exists which does not contain nitrogen.

[71] This is less on the whole than what has been found in subsoils by
Continental investigators. Thus, for example, A. Mueller found the
average of a number of analyses of subsoils to be .15 per cent., and the
late Dr Anderson found the nitrogen in the subsoil of different Scottish
wheat-soils to run from .15 per cent to .97 per cent.

[72] See Appendix, Note II., p. 156.

[73] "Under prolonged kitchen-garden culture the subsoil becomes
enriched with nitrogenous matter to a far more considerable depth; this
has been shown by the analyses of the soil of the old kitchen-garden at
Rothamsted. This is doubtless due to the practice of deep trenching
employed by gardeners."--R. Warington, 'Lectures on Rothamsted
Experiments.' U.S.A. Bulletin, p. 24.

[74] The comparatively insignificant effect the addition of various
nitrogenous manures have in increasing the total soil-nitrogen is
strikingly illustrated in the tables given in the Appendix, Note IV., p.
157.

[75] See Storer's Agric. Chem., vol. i. p. 357.

[76] See Chapter IV., Appendix, Note VII., p. 198.

[77] See Appendix, Note III., p. 157.

[78] See Appendix, Note IV., p. 157.

[79] See Appendix, Note I., p. 155.

[80] The original source of the nitrogen in the soil must have been the
nitrogen in the air. When plants first begin to grow on a purely mineral
soil, they must obtain nitrogen from some source. The small traces
washed down in the rain will supply sufficient nitrogen to enable a
scanty growth of the lower forms of vegetable life; whereas these by
their decay furnish their successors with a more abundant source