[15] It may be pointed out that, while the amount of ammonia washed down by the rain is small, Schloesing has found in some recent experiments that a damp soil may absorb from the air in the course of a year 38 lb. of combined nitrogen, chiefly ammonia, per acre. See p. 132.
[16] The example, set by Germany, has been followed by other countries in which well-equipped research stations now exist. Perhaps the most striking example of the rapid development of the means of agricultural research is furnished by the United States of America. At present over fifty agricultural experiment stations, more or less well equipped, exist at present in that country, all liberally supplied by State aid. The earliest to be founded, it may be added, was that at Middletown, Connecticut, the date of its institution being 1875.
[17] It may thus claim to be the second oldest experimental station, that instituted by Boussingault at Bechelbronn in Alsace being the oldest.
[18] For an account of the Rothamsted experiments, and a short biography of Sir John Lawes, the reader is referred to a pamphlet by the present writer, entitled 'Sir J. B. Lawes, Bart., LL.D., F.R.S., and the Rothamsted Experiments' ('Scottish Farmer' Office, 93 Hope Street, Glasgow).
[19] Of these numerous elaborate experiments, perhaps those which have attracted the most widespread interest amongst agriculturists have been those carried out on the growth of wheat on the same land year after year for a period of nearly fifty years. The important light which this series of experiments has thrown upon the theory of the rotation of crops, and the subject of the manuring of cereals, is very great.
[20] Associated in some cases with phosphorus and sulphur.
[21] It must be pointed out that plant-respiration does not take place only during the night-time. It probably goes on at all times, but it is only during the night-time that its action is apparent, as the reverse process of carbon assimilation, which goes on at an incomparably greater rate, masks its action during the daytime.
[22] The length of the day has an important influence on plant-growth, as is evidenced by the rapid growth of vegetation in Norway and Sweden. In these countries there is a late spring, and a short and by no means hot summer, but a very long period of daylight.
[23] A point of great interest which these experiments elucidated is that nocturnal repose is not absolutely necessary for the growth and development of all plants.
[24] See pp. 15 and 22.