For very delicate shading and tinting, stipple may be employed, but the dots must be quite definite, sufficiently large to stand reduction, and not too close together (Figs. 18, 28c, and 32). A particularly good example of this method will be found in Butler's paper on _Allomyces_ in the Annals of Botany, 1911, vol. 25. Dots have also been employed in Fig. 28c (p. 69). With regard to local colour; this may be indicated by shading, by a white space, or by a black space. Hitherto, drawing with black ink on white paper alone has been considered, but the reverse is equally available; much can be expressed by drawing with white ink on black paper. Drawing in white upon a black ground is not frequently attempted, but an excellent example by Miss Janet Robertson is shewn in figure 16, which is well worthy of study, since it illustrates to a nicety some of the means at the disposal of the draughtsman for line blocks. The black surface is best obtained by the use of a waterproof Indian ink applied with a brush to a white surface, the drawing being made with a dense white ink, using a pen or a brush. The white ink may be made by diluting any good opaque white water-colour paint, or process white may be used. The composition of this should be zinc oxide or baryta, for these do not darken with age; the author once used for this purpose a white pigment which proved excellent at the time; the drawings, however, subsequently turned dark brown owing to the fact that the basis of the paint was apparently a compound of silver. [Illustration: Fig. 16. _Neuropteris Heterophylla_. A line reproduction of a drawing by Miss Janet Robertson.] The top part of the drawing (Fig. 16), shewing the general morphology of the plant, was drawn with a brush charged with white ink upon a black ground. In the simplest possible way relief has been obtained by representing the leaflets of the nearer fronds by white spaces, whilst those further away are represented by white outlines. An enlargement of a frond is shewn on the lower part of the picture, and here the parts are represented in black on a white ground. The leaflets are in black outline and the fruits are made to stand out, as in the upper part, by the use of local colour--in this instance black--their shape being indicated by the curve of the higher lights. In brief, a very effective drawing has been made by the simplest use of the white line, the white space, the black line and the black space. [Illustration: Fig. 17. _Fucus volubilis_, var. _Flexuosus_, a seaweed. (From a drawing by Miss Baker.)]