78 
PROFESSOR W. C. WILLIAMSON ON THE ORGANIZATION 
c. Medullary vessels. 
d. Ligneous zone. 
/. Medullary rays. 
g. Inner bark. 
h. Middle parenchymatous bark. 
Jc. Prosenchymatous outer bark. 
1. Leaves. 
n. Root-bundles of vessels. 
o. Rootlets. 
r. Cicatrices of strobili. 
s. Strobilus-axis. 
t. Bracts of strobilus. 
u. Sporangia. 
v. Sporangiophores. 
w. Spores. 
x. Lateral branch. 
PLATE I. 
Fig. 1. Transverse section of a very young twig from Oldham, showing the primitive 
vascular bundle, the equivalent of the medullary vessels of the Lycopodiacece, 
magnified 30 diameters. 
Fig. 2. Similar section of a twig, with one exogenous layer of the ligneous or vascular 
zone surrounding the primitive bundle, enlarged 30 diameters. 
Fig. 3. Similar section of a young branch with two exogenous layers, magnified 30 
diameters. 
Fig. 4. Similar section of a young branch, with double bark-furrows and three exo- 
genous layers, magnified 30 diameters. 
Fig. 5. Longitudinal section of a young branch, with three exogenous layers, magnified 
30 diameters. 
Fig. 6. One of the vessels of the ligneous zone of fig. 5, seen on the side parallel with 
the medullary rays, magnified 420 diameters. 
Fig. 7. Cells of the inner bark, from a longitudinal section like fig. 5, magnified 200 
diameters. 
PLATE II. 
Fig. 8. Longitudinal section of some of the prosenchymatous cells of the outer bark, 
magnified 130 diameters. 
Fig. 9. Transverse section of the vascular axis and inner bark of a more matured stem, 
magnified 30 diameters. 
Fig. 10. Similar section to the last, but of a more fully developed stem and with a thicker 
inner bark, magnified 30 diameters. 
Fig. 11. Transverse section of a yet further developed stem, exhibiting a secondary 
series of concentric exogenous growths, magnified 30 diameters. 
Fig. 12. Similar section to fig. 11, with very large vessels in the inner exogenous 
laminae, magnified 30 diameters. 
Fig. 13. Tangential section of two vessels of the exogenous layers of the same specimen 
as fig. 9, showing the medullary rays, magnified 125 diameters. 
