300 
PROFESSOR W. C. WILLIAMSON ON THE ORGANISATION 
Index to the Plates. 
Letters of reference to the figures of Heterangium Tiliaeoides. 
Plates 21 and 22, fig’s. 1-19. 
7 O 
A, Vasculo-cellular medullary axis. 
a, Medullary cells. 
h, ,, vessels. 
B, Exogenous xylem. 
c, Vascular wedges or bundles. 
d, ,, laminae. 
e, f, Vessels or tracheidsV 
g, Primary medullary rays. 
k, Secondary „ „ 
i, Cambial line. 
C, Phloem zone. 
h, Phloem of the vascular bundles. 
l, „ tubes. 
m, ,, parenchyma. 
n, Primary phloem rays. 
o, Secondary phloem rays. 
D, Cortex. 
p, Inner cortex. 
r, Outer ,, 
s, Cortical cells. 
t, Cortical bands of sclerenchyma. 
u, Double vascular bundles. 
w, Lateral branch. 
5 55 55 
* I Hare employed these two terms throughout the memoir without attempting to determine which 
of them may be applicable to the objects described. It is impossible to distinguish vessels from traclieids 
in these Carboniferous fossil plants. 
