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 28b, and when such cells are relatively few in number, this method has much to recommend it since a greater relief is obtained.

Fig. 28.

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 28c. Here the thickness of the cells of the wood is represented by broad black lines, the middle lamellæ 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.

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.*

*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.