FOOTNOTES:
[1] The History of the Chemical Elements. By Sir Henry E. Roscoe, F.R.S. (Wm. Collins, Sons, & Co.)
[2] Van Helmont's science was, however, of an extremely rudimentary nature, as may be evidenced by the belief he entertained that the smells which arise from the bottom of morasses produce frogs, slugs, leeches, and other things; as well as by the following recipe which he gave for the production of a pot of mice: "Press a dirty shirt into the orifice of a vessel containing a little corn, after about twenty-one days the ferment proceeding from the dirty shirt, modified by the odour of the corn, effects a transmutation of the wheat into mice." The crowning point in this recipe, however, lay in the fact that he asserted that he had himself witnessed the fact, and, as an interesting and corroborative detail, he added that the mice were born full-grown. See 'Louis Pasteur: His Life and Labours.' By his Son-in-law. Translated by Lady Claud Hamilton. (Longmans, Green, & Co.) P. 89.
[3] He then goes on to relate a number of experiments by Cornelius Drebel and Albertus Magnus, showing the refreshing power of this balsam, and then those of Quercitan with roses and other flowers, and his own with nettles.
[4] Priestley, however, did not realise that carbonic acid gas was a necessary plant-food; on the contrary, he considered it to have a deleterious action on plant-growth. Percival was really the first to point out that carbonic acid gas was a plant-food.
[5] It is recorded as an instance of the scientific enthusiasm of the man, that he was wont to carry about with him bottles containing oxygen, which he had obtained from cabbage-leaves, as also coils of iron wire, with which he could illustrate the brilliant combustion which ensued on burning the latter in oxygen gas.
[6] For a full account of Sénébier's researches, see 'Physiologie végétale, contenant une description des organes des plantes, et une exposition des phénomenes produits par leur organisation, par Jean Sénébier.' (5 tomes. Genève, 1800.)
[7] How Crops Grow. By Professor S. W. Johnson. Macmillan & Co. (Introduction, p. 4.)
[8] See p. 40 to 45.
[9] Elements of Agricultural Chemistry, in a course of Lectures for the Board of Agriculture. By Sir Humphry Davy. (London, 1831.)
[10] This department of agricultural research was subsequently carried on by Sprengel, Schübler, and others.
[11] Born in Paris, 1802; died 11th May 1887.
[12] See p. 40.
[13] While much of Boussingault's work was carried out previous to the year 1840, he continued to enrich agricultural chemistry with numerous valuable contributions up till the time of his death. It may be well here to mention the names of his most important contributions to agricultural science, made subsequent to 1840.
In 1843 he published, in a work entitled 'Economie Rurale,' the results of his numerous experiments and researches. This work is well known to English agriculturists from an English translation which appeared in 1845 (Boussingault's 'Rural Economy,' translated by G. Law. H. Ballière, London).
In 1860 appeared the first volume of his last great work, 'Agronomie Chimie Agricole et Physiologie' This work, which consisted of seven volumes, was not finished till 1884. He died on the 11th of May 1887. It may be added that the Royal Society of London awarded him the Copley medal in 1887.
[14] See British Association Proceedings, 1880, p. 511.
[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.
[25] See p. 22.
[26] See Chapter III., pp. 120 and 131.
[27] Further reference is made to this subject in Chapter III., p. 136.
[28] See p. 6.
[29] See Phil. Trans., Part II., 1861, pp. 444-446. Lawes & Gilbert. Schloesing has found in the air in the neighbourhood of Paris 1 lb. of ammonia in 26,000,000 cubic yards; while Müntz found only about half that amount in a similar quantity of air on the top of the Pic du Midi.
[30] See Chapter III., pp. 119, 120; Appendix, p. 155.
[31] Some recent experiments by Dyer and Smetham would seem to show that comparatively small quantities of ammonia in the air prove actually hurtful to plant-life. Thus they found that one volume of ammonia in 1000 volumes of air was fatal to hardy plants; while one volume in 3000 volumes killed tender ones.
[32] According to the experiments of Hellriegel and Wollny. The quantity, it may be added, varies with the leaf-surface and the length of the period of growth of the plant. It is greatest with clovers and grasses, and least in the potatoes and roots.