32 
be convinced. The axis of the stem cannot be considered as a true medulla 
or pith, inasmuch as it is composed not of simple cells, but of elongated 
utricles of various sizes, irregularly arranged, and having thin walls 
marked with scalariform bars. The tissue of the wooden cylinder consists 
of long scalariform vessels, which increase in size from the inner margin 
to the outer, this increase being sufficient to meet the requirements of the 
enlarged circumference, with the help of only a few additional series of 
vessels. As there is no true medullary cellular tissue in the axis 
60 there are no medullary rays passing through this cylinder. 
In radial sections an appearance 13 seen singularly resembling, to 
the naked eye, the "silver grain," produced in dicotyledonous woods 
by the medullary rays ; but this arises from a very different cause. The 
woody cylinder is surrounded by a great thickness of cellular tissue, which 
extends to the exterior of the stem, and is composed of three distinct 
and separable zones. The cell walls of all the three zones are without 
markings of any kind. These zones are traversed by the vascular bundles, 
which rise from the outside of the interior wood cylinders and pass to the 
leaves and branches. Each bundle consists of fine scalariform vessels and 
terminate in the points seen in the areoles of the stem, which are the scars 
of the leaves." 
Stigmarioid Eoots have been determined to belong to Lepidodendron as 
well as to Sigillaria, and their whole structure supports this determination. 
The roots of Lepidodendron must have presented in their crowded and long 
rootlets an immense surface for the absorption of moisture ; and in their 
great abundance of lax cellular tissue possessed the means of containing 
this moisture, and transmitting it to the foliage. The leaves were simple, 
lanceolate, acute, and sessile. They had a single medial nerve, and when 
found separated from the branches, are called Lepidophylla. The younger 
branches were densely covered with leaves ; the scars left on the trunk 
after they perished give the numerous beautiful markings by which the 
species have been distinguished. The fruit was a strobilus formed from a 
shortened branch, the leaves of which are converted into scales, that 
support on their upper surface a single large sporangium, or perhaps as in 
the Flemingites several small ones . There appear to be both macrospores 
and microspores in the same sporangium. Specimens of Lepidostrobus, as 
the fruit is called, have been found attached to the branches of Lepido- 
dendron. In tracing the affinities of this genus we have the safest guide 
in the organs of fructification. The sporiferous strobilus shows that it is 
a true cryptogam ; and in general appearance and arrangement of parts the 
