Plate 2 is an example of a chromolithograph. Miss O. Johnston first drew the outline of the plant, which was phototransferred on to the stone. An impression was then pulled and tinted by the artist, and from this tinted impression the colour stones were made by the lithographer. It may be added that only three colours were used in printing the plate. Examples: Baur: _Einfuehrung in die experimentelle Vererbungslehre_ (Plate 1). Berlin, 1911. Bruce and others: _A Note on the Occurrence of a Trypanosome in the African Elephant_. Proceedings of the Royal Society of London, B. Vol. 81, 1909. Cropper: _The Development of a Parasite of Earthworms_. _Id._ Vol. 85, 1912. Oliver: _On Sarcodes sanguinea_. Annals of Botany, Vol. 4, 1889-1891. Rubbel: _UEber Perlen_ ... Zoologische Jahrbuecher, Vol. 32, 1911-12. Biometrika, 1906-7, Vol. 5, Plate 23. Mention has been made of the value of a knowledge of colours. The subject is much too extensive to be considered adequately on the present occasion even if it were desirable; its importance, however, warrants a few passing remarks.[A] [Footnote A: See Ridgway: _Color Standards and Color Nomenclature_.] No two people will describe in the same way the colour of, say, a rose petal; both will have a different conception of the colour "crimson." The majority have but a limited sense of colour, and even when this faculty is possessed, the personal equation looms large; further, the ordinary names of colours are quite inadequate for descriptive purposes. For these reasons the importance of a scientific system of colour nomenclature and colour standards is all important. By the use of such a scheme, the exact colour of an object can be found by comparison with an adequate chart, and the name there given will convey to others exactly what colour is described or desired. The plumage of a bird or the colour of a flower can thus be described correctly, and an author can indicate exactly the colour desired in certain parts of a chromolithograph or other reproduction in colour. [Illustration: PLATE 2.--GERANIUM COLUMBINUM. A chromolithographic reproduction of a drawing by Miss O. Johnston] PHOTOLITHOGRAPHIC PROCESSES.--Of these methods of reproduction there are several, their value lying in the fact that the originals can be reduced or enlarged with the greatest of ease. The general principles are as follows. A photographic negative is taken of the original drawing and a positive made on a film of bichromate gelatine. Wherever light reaches the film, the gelatine is rendered more or less insoluble according to the intensity of the light acting upon it; through the dark parts of the negative but little light will pass, so that the gelatine will remain soluble.