232 
PEOFESSOIl W. C. WILLIAMSON ON THE OEOANIZATION 
Description of the Plates. 
The same letters are employed throughout to represent, as far as possible, what 
appear to be homologous parts, in accordance with the following plan : — 
a. Medullary axis. 
b. Cells of medullary axis. 
c. Vessels of medullary axis. 
d. Ligneous zone. 
e. Vessels of ligneous zone. 
f Medullary rays. 
g. Innermost part of the bark. 
h. Middle parenchymatous part of the 
i. Outer or prosenchymatous part of thebark. 
Jc. Tubular portion of i. 
l. Bases of leaves or petioles, detached or 
coalesced into an epidermal layer. 
m. Bundles of vessels going to the leaves. 
n. Bundles of vessels going to the rootlets. 
o. Bootlets. 
p. Indentations of epiderm in which roof 
bark. lets are planted. 
r. Scars or cicatrices from which cones are supposed to have fallen. 
Where not otherwise specifically mentioned, the specimens represented are in the 
author’s cabinet. The collectors from Avhom some of the fossils were received are 
named, but the sections, in these examples, are also in the author’s cabinet. 
Plate 
XXIV. fig. 1. Lejpidodendron selaginoides, a young branch, transverse section, magnified 
6 diameters. Mr. Butterworth’s cabinet. 
„ fig. 2. Lepidodendron selaginoides , longitudinal section of fig. 1, magnified 4 
diameters. Mr. Butterwortii’s cabinet. 
„ fig. 3. Lepidodendron selaginoides , part of medullary centre of fig. 1, magni- 
fied 200 diameters. 
,, fig. 4. Lepidodendron selaginoides , part of medullary centre of fig. 2, magnified 
70 diameters. 
,, fig. 5. Lepidodendron selaginoides , tangential section of outer bark immediately 
below the epiderm, magnified 7 diameters. Mr. Butterworth’s cabinet. 
„ fig. 6. Lepidodendron selaginoides , tangential section of outer layer of epiderm 
at the base of the petioles, magnified 7 diameters. Mr. Butterworth’s cabinet. 
XXV. fig. 7. Lepidodendron selaginoides, subepidermal surface of outer bark, nat. size. 
„ fig. 8. Transverse section of central axis, woody zone, and part of the inner bark 
of one form of the Sigillaria vascularis of Mr. Binney’s memoir, magnified 
10 diameters. Mr. Butterworth’s cabinet. 
„ fig. 9. Longitudinal section of fig. 8, magnified 10 diameters. Mr. Butter- 
worth’s cabinet. 
„ fig. 10. Tangential section of the woody zone of the same type as fig. 8, showing 
the medullary rays. 
„ fig. 11. Prosenchyma of the bark of fig. 10, magnified 400 diameters. 
„ fig. 12. Lepidodendron , transverse section, nat. size. Mr. W. B. Dawkins’s 
cabinet. 
