Chapter 4

(1) Baron de Cuvier's Theory of the Earth. New York, 1818, p. 123.

(2) On the Organs and Mode of Fecundation of Orchidex and Asclepiadea, by Robert Brown, Esq., in Miscellaneous Botanical Works. London, 1866, Vol. I., pp. 511-514.

(3) Justin Liebig, Animal Chemistry. London, 1843, p. 17f.