[1] Svante Arrhenius: “The Destinies of the Stars.” Translated by J. E. Fries. Putnam, 1918.

[2] F. Soddy: “Matter and Energy,” 1912, p. 194.

[3] A. G. Tansley: “Types of British Vegetation,” 1911, p. 63.

[4] H. B. Guppy: “Plants, Seeds, and Currents in the West Indies and Azores,” 1917, p. 425.

[5] W. B. Barrows: “Seed-planting by Birds.” Report of the Secretary of Agriculture, U.S.A., 1890, p. 281.

[6] See A. H. Church: “The Plankton-phase and the Plankton-rate,” Journal of Botany, June, 1919, supplement.

[7] G. H. Carpenter: “Insects: Their Structure and Life,” p. 300.

[8] W. B. Bottomley in “The Exploitation of Plants,” edited by F. W. Oliver, 1917, p. 12.

[9] To be accurate, certain groups of Bacteria, the lowest forms of organized life, must be excluded. They appear capable of building up their bodies directly out of inorganic substances.

[10] F. J. Hanbury and E. S. Marshall: “Flora of Kent,” 1899, p. xxxv.

[11] A. F. W. Schimper: “Plant Geography” (English translation, 1903), p. 719.

[12] A. F. W. Schimper: “Plant Geography” (English translation, 1903), p. 41.

[13] See Agnes Arber: “Aquatic Angiosperms: the Significance of their Systematic Distribution,” Journal of Botany, 1919, p. 83.