210 
PROFESSOR W. C. WILLIAMSON ON THE ORGANISATION 
Index to Plates 5-8. 
Plate. 
Fig. 
1 Pages on w’nicli 
references are 
made to the 
j figures. 
5 
1 
Part of a transverse section of a stem of Lepidodendron 
Harcourtii : a, part of the medulla ; b, h, portions of 
the medullary (or non-exogenous) vascular cylinder ; 
h', a segment of the cylinder becoming detached at 
the points h" , h" to supply a branch. X 30. 
Cabinet number, 1654 . . . .. 
1 
196, 201 
5 
2 
The portion 6, b, a, of fig. 1, after the segment b' has 
become detached. X 30. Cabinet number, 1656 
197, 201 
5 
3 
The segment, fig. 1, b', after its detachment from 
fig. 2 ; a, remains of the medullary cells. X 30. 
Cabinet number, 1656 . 
197, 201 
5 
4 
The segment, fig. 3, in process of conversion into a 
terete vascular bundle. X 30. Cabinet number, 
1658 . 
197, 201 
5 
5 
The same segment intersected yet higuer up in its 
ascending course ; a, the point from which the 
medullary cells of fig. 3, a, have almost entirely 
disappeared ; b', b', the points of the medullary 
vascular ring corresponding to b', b' of fig. 3, but 
which have now converged. X 30. Cabinet 
number, 1659 . 
196, 201 
5 
6 
The same segment at a yet higher point, where it has 
23assed into the cortex as the vascular bundle of a 
distinct branch, from which all traces of medullary 
cells have disappea.red. X 30. Cabinet number, 
1661. 
Lepidodendron niimduni. Will. 
196, 201 
0 
7 
Transverse section of a very young shoot of Lepido¬ 
dendron mundiini, Will. : 5, the vascular bundle, 
not yet developed into the hollow medullary 
vascular cylinder ; c, the outer cortex. X 80. 
Cabinet number, 4166. 
197, 204 
6 
8 
The vascular bundle b, of fig. 7, enlarged, x 220 . 
197, 205 
