120 Contributions towards Establishing the General Character 
second, a double parenchymous zone; third, a hollow vascular cylinder ; 
and fourth, a pith. It has been customary to consider the axis or pith 
as eccentrically situated, but from certain reasons which have been 
given in a former part of these contributions, 1 am disposed to think 
that this was not a character of the plant when living : the central situa- 
tion of the pith will therefore be assumed in the following description. 
The cuticle, according to some sections, orignally published by Wi- 
tham, Lindley, and Hutton, is thin, and consists of a form of prosenchy- 
mous tissue, being elongated longitudinally, and arranged in a radial man- 
ner transversely. 
In a section of Lepidodendron, an inch and three-eighths in diameter, 
the outer part of the double parenchymous zone is a quarter of an inch 
in thickness: it is composed of a tissue which bears a close resemblance 
to the parenchyma of the petiole of the Spread-Eagle Fern, (Pteris agui- 
lina.) The cells are large, so much so, as to be observed by a common 
magnifier: on the transverse section they are either round or polygonal, 
in the last form; the sides of the figure are in general equal. On the lon- 
gitudinal section the cells are somewhat elongated: they in general taper 
off rather suddenly at both ends, so as to terminate in an obtuse cone, 
and they display a tendency to arrange themselves in linear series. The 
inner part of the zone is about half as broad again as the outer one; judg- 
ing from some which are here and there displayed, its constituent cells 
appear to be much smaller and more delicate than the last: they are 
somewhat of the same form on the transverse section ; but on the longi- 
tudinal one they are quadrangular, and they run decidedly in linear 
series. The tissue of this part is very rarely preserved; its character 
has therefore not been made out so satisfactorily as could be desired. 
Brongniart, in his restoration of the double zone, represents its cells of 
the same form longitudinally as they are transversely, which certainly is 
not the case in any of my sections. 
The hollow vascular cylinder, which is a little less than an eighth of an 
inch in thickness, is composed of polygonal tubes, having no order in 
their arrangement, except that which pertains to difference in diameter. 
These tubes have the whole of their walls transversely marked with fine 
lines or bars, similar to thosewhich characterise the vessels of the medul- 
lary sheath of Sigillaria elegans: those which are situated on the inner 
part of the cylinder are as large again in diameter as the cells composing 
the outer part of the double zone; but they become gradually smaller 
in the outward direction, until within a short distance of the outer side 
of the cylinder, and there they become, all on a sudden, considerably 
reduced. Inno part does the vascular cylinder exhibit the least appear- 
ance of lateral openings. 
From the outside of the vascular cylinder, and at certain points, arise 
a number of cords which pass into the leaves: they are made up of the 
smallest sized vessels. The outer part of the double zone is furnished 
with a number of openings, which serve as passages for these leaf cords; 
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