950 
Hig. 1. 
Fig. 2. 
Fig. 3. 
Fig. 4. 
Fig. 5 
Fig. 6. 
PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
PLATES 77-85.—Figures from camera-lucida drawings executed by 
Mr. Grorce BREBNER. 
PLATE 77. 
Calamites. 
‘Transverse section of a very young twig. The pith is nearly solid, but slightly 
disorganized near the centre. There are seven vascular bundles, each with its 
canal. In most of the canals rings can be seen (as at px), which are the 
remains of the primitive trachese. Secondary wood, both fascicular and inter- 
fascicular, has just begun to be formed. The simple cortex is well preserved. 
C.N..116*, 100. 
Transverse section of a larger twig, but at a still earlier stage of development. 
The pith is hollow. There are twelve bundles, each with a canal, on the outer 
edge of which is the primary xylem. No secondary tissue has yet appeared. 
The cortex shows little differentiation. This is another section of the same 
specimen which is shown in Plate 72, photograph 1. C.N. 1561. x 50. 
Part of a transverse section of a larger and more advanced stem, the same as 
that of which another section is shown in Plate 72, photograph 2. A broad 
outer zone of pith is preserved. Two vascular bundles are shown. About 
twelve layers of secondary wood have been formed. The narrower elements 
belong to the secondary medullary rays. Interfascicular wood is already 
formed across the principal rays. The phloém and cambium are disorganized, 
but their position is evident (ph). The well-preserved cortex is differentiated 
into two distinct layers. C.N. 14. x 50. 
Oblique section of a young branch; its cortex was preserved, but is not 
shown. The pith is hollow. There are twelve vascular bundles. [n the 
canal of each bundle the fragmentary rings and spirals of the primitive 
trachez, or protoxylem, are seen, as at px. They sometimes extend to the 
iuner margin of the canal (see especially the bundle marked a). Only the 
primary xylem of the bundles exists at this stage. C.N. 1002. x 100. 
Part of a radial section passing through the primary wood of a bundle. On 
the left are pith-cells. In the middle is the canal, which is still partly filled 
by the disorganized remains of the protoxylem (px). The trachee are partly 
annular, partly spiral. Towards the right they become more continuous. 
Still further to the right we see the persistent scalariform trachez (sc) of the 
primary wood external to the canal. C.N. 20a. x 200. 
Part of a transverse section, showing a leaf-trace bundle passing out hori- 
zontally through the secondary wood. On the left are pith-cells; pa, proto- 
xylem of a bundle passing into the next internode. The reticulated trachese 
