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 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, 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.]
A half-tone can be put on to a line block during its manufacture. All that the draughtsman has to do, is to indicate by blue pencil lines those parts on which he requires the dots, which give the half-tone, to be placed, and to select the pattern of the stipple he desires to be used. The result may appear somewhat mechanical since the dots are regularly arranged, but a drawing sometimes may be considerably improved by this means if used with judgment. It is frequently employed in representing drapery, and many examples may be found on those pages of newspapers devoted to ladies' dress (Fig. 31; see also Fig. 32).