9352 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
Remains of the phloém (ph.) are seen. The cortex consists of two distinct 
layers (c and c’); the outer layer becomes more sclerenchymatous towards the 
periphery. C.N.118*. x 50. 
Fig. 13. Another part of the same section showing a phloém-group (ph). The 
cambium (cb) between wood and phloém is also preserved, and the phloém 
itself is complete, though crushed. The large cells above belong to the cortex 
(c) GN. 118%. x 150. 
Fig. 14. From the same section, showing a small portion of wood (x), cambial cells 
(cb) and their derivatives, and cortex (c). C.N.118*. x 150. 
The figs. 12, 13, and 14 are from the section, a part of which is shown in Plate 72, 
Photograph 3. 
PLATE 79. 
Calamites. 
Fig. 15. Tangential section passing through a principal medullary ray near the pith. 
On either side are seen tracheides and one or two secondary rays (as at 7). 
The principal ray is entirely parenchymatous; the elements towards the 
middle are quite short; those near the edges are narrower and more 
elongated (m). C.N. 65. x 50. 
Fig. 16. From another section of the same stem, showing a principal ray further 
towards the exterior. The whole ray is narrower; the marginal cells (m) are 
more elongated, and are already partly replaced by tracheides. The ray to the 
left (r) may probably have been cut off from the principal ray by interpolated 
tracheides. C.N. 66. x 50. 
Fig. 17. A third section of the same stem, still further towards the exterior. The 
principal ray is no longer continuous, but is completely broken up by inter- 
polated tracheides. Some of its isolated parts (7) are quite similar to second- 
ary tays, C.N. G7. X50, 
Fig. 1§. Part of a transverse section showing cortex, and a small part of the secondary 
wood (x); the gap between them was caused by the growth of a Stigmarian 
rootlet, which is not figured. Remains of the phloém (pA, are shown. Many 
of the cortical cells, especially those at a short distance from the interior, show 
recent tangential divisions, indicating the formation of periderm (pd). From 
a slide (No. 6) prepared by Mr. Lomax, in the possession of D. H. Scort. 
x 70; 
Fig. 19. Part of a median section, passing through a diaphragm. The cells towards 
both surfaces of the diaphragm have undergone regular tangential divisions 
(best shown on the upper surface), forming a layer of periderm. O.N. 132***, 
xX 30. 
Fig. 20. Part ofa transverse section passing tangentially through the base of a branch, 
