212 
PROCESSOR W. C. WILLIAMSON ON THE ORGANISATION 
Plate. 
Pig. 
Pages on which 
references are 
made to the 
figures. 
Lepidodendon intermedium, Will. 
7 
1 
16 
Transverse section of a stem in whicli the more internal 
tracheids of the medullary vascdar cylinder, h, are 
loosely intermingled with the cells of the medulla, a. 
The exogenous zone, d, is composed of extremely 
small tracheids arranged in radiating lines. This 
zone is encased in a zone of the uniformly small 
cells of the inner cortex e. Cabinet number, 417. 
X 40. 
198, 202 
7 
17 
Part of a tangential section of the exogenous zone, d, of 
fig. 16, exhibiting numerous meandering tracheids, 
d', intermingled with relatively large cells, d”. 
Cabinet number, 419. X300 . 
198, 202 
1 8 
1 
18 
Part of a vertical section made through the centre of 
the medullary vascular cylinder : a, vessels of the 
medullary cylinder, fig. I6h; d, exogenous zone; 
e, innermost cortex. Cabinet number, 419. X 300 
Lep){dodendron Spencem, Will. 
198 
8 
1 
1 
19 
Transverse section of a branch: a, central vascular 
cylinder devoid of any true medulla ; e, thin zone of 
the inner cortex, most of which has disappeared; 
f, the middle cortex ; f, prominence of the middle 
cortex, through which a foliar vascular bundle has 
issued ; f", masses of dense thick-walled cells, many 
of which in each mass have become disintegrated. 
These dark masses have alternated with radiating 
bands of cells, f"', of larger size, and with thinner 
walls. Cabinet number, 19Z>. X 25. 
1 
[ 
199 
7 
20 
A peripheral point, like /' of fig. 19, showing the 
tracheids of the foliar bundles at f', the inner 
cortex af e, and the middle cortex at f. Cabinet 
j 
number, 419n. X 50. 
199 
