The walls of the various elements may be represented by lines of more or less equal breadth, but in those cases where the walls are particularly thick, _e.g._, the elements of the wood, the thickening may be represented by an additional line. This is seen in Fig. 27, in which it will be noticed that the middle lamellae of the wood-elements are represented by black lines. [Illustration: Fig. 27. (From Butler's paper on Gummosis of _Prunus_ and _Citrus_. _Annals of Botany_, 1911, Vol. 25).] This is a particularly good drawing, but, unfortunately, it has been over reduced. On the other hand, the various tissues may be represented by lines of varying breadths, the thickest walled cells having the same double contour as in the above, but with the addition of local colour in the shape of diagonal shading. This is not uncommonly found in papers dealing with the anatomy of plants by French authors; it is illustrated in Figure 28 _a_. If preferred, such thick-walled elements may be entirely represented by thick black lines as in Figure 28_b_, and when such cells are relatively few in number, this method has much to recommend it since a greater relief is obtained. [Illustration: Fig. 28 _a_ _b_ _c_ A transverse section to shew the vascular cylinder of the root of the spinach, _c_ is somewhat older than _a_ and _b_.] Finally, an attempt may be made to draw in a more detailed fashion as in Figure 28_c_. Here the thickness of the cells of the wood is represented by broad black lines, the middle lamellae being left white. The lines marking the boundaries of the other cells vary slightly in thickness, but this is to a great extent masked by the representation of the cell contents, which consist entirely of dots in the case of the protoplasm, whilst the nuclei are represented by dark ovals--black relieved with small white areas. By varying the size of the dots and their distance apart, varying densities can be indicated. It has been mentioned above that it is possible to reproduce fine detail by means of the line block; this is illustrated in Figs. 29 and 30. [Illustration: Fig. 29] Fig. 29, which illustrates a stage in the division of a nucleus, was drawn with black crayon on a rough-grained piece of Whatman's water-colour paper. The cytologist will, doubtless, criticize its coarseness, but it may be mentioned that the roughest paper at hand was designedly employed in order to illustrate the point raised. That a finer grained paper will give more delicate results is shewn by Fig. 30, which is a reproduction of a drawing, kindly lent by Dr. W. G. Ridewood, made with ordinary lead pencil on grained Bristol board. Its delicacy is obvious, and at first sight it could easily be mistaken for a lithograph.[A] [Footnote A: Many similar examples will be found in Ridewood's memoir _On the Cranial Osteology of the Clupeoid Fishes_, Proc. Zoo. Soc., Lond., 1904, vol. 11, p. 448.] [Illustration: Fig. 30]