''r^i.^'JcT^^^^ Royal Mzcroscojpical Society, 181 
cells of this layer are small and spherical, with very delicate walls. 
They were the first portion of the stem structures to decay, and 
almost invariably the cellular rootlets from Stigmarioid and other 
roots pushed their way into these decaying cavities, and being there 
preserved have been mistaken by several observers for portions of 
the tissues of the stem. The vascular bundles, described as pene- 
trating the vascular cylinder, pass in an upward and then in an 
outward and upward direction through this layer of parenchyma. 
Frequently these delicate bundles have been involved in the decay 
which destroyed the mass of the cells through which they passed, 
and no record of them remains from their leaving the vascular 
cylinder until they enter the outer cylinder of more compact tissue. 
In the specimen figured I have counted twenty-four vascular bun- 
dles, either closely adpressed to or adjoining the vascular cylinder. 
The next structure in the stem is a layer of larger and thicker 
walled parenchyma (Figs. 1 d and 2 d), which, by a gradual length- 
ening of the cells, and a decrease in their diameter, becomes changed 
into the regular^ arranged prosenchyma of the circumference 
(Figs, le and 2e). These outer cells agree in every respect with 
true wood cells, being greatly elongated and having pointed extre- 
mities, and the method in which they are arranged is very much that 
of the wood cells in exogenous stems. No indication of any hori- 
zontal cellular structure has been detected in this prosenchymatous 
cylinder corresponding to what has been described in the scalariform 
tissue. The vascular bundles, accompanied with a certain amount of 
cellular tissue, pass upwards and outwards through it to the leaves. 
In the specimen figured, the outer portion of the prosenchyma 
(Fig. If), consisting of six cells in depth, has a shghtly different 
aspect from the rest, and has been easily detached from it. In posi- 
tion, appearance, and the ease with which it separates from the older 
structure, it answers to the younger growing portion of the wood in 
exogenous stems, and may have had a corresponding significance. 
Outside this there is a layer of small thick-walled parenchyma 
(Fig, 1 gf), from eight to twelve cells thick, forming the external bark. 
The vascular bundles can be traced through all these layers 
into the leaf. As they approach the surface of the stem they have 
a somewhat circular transverse section. A small quantity of cellu- 
lar tissue occupies the centre of the bundle. It is its termination 
in the centre of the characteristic scar of this species which gives 
the circular depression shown in the figures of the fossil. 
The bases of the leaves are persistent, and are composed of 
roundish parenchyma (Fig. Ih). The leaves themselves seem to 
have been deciduous, for in a specimen where the section passes 
through the end of the vascular bundle, the surface of the rhom- 
boidal elevation which supported its leaf is cicatrized, being composed 
of a layer of small thickened cells. 
