294 
POPULAR SCIENCE REVIEW. 
walls marked with scalariform bars. This is so different a 
structure from the pith of a dicotyledon that it can only be 
compared to it from occupying the same position in the stem. 
It is surrounded by a compact cylinder consisting of long sca- 
lariform vessels, which somewhat increase in size from the inner 
margin to the outer, this increase being sufficient to meet the 
requirements of the enlarged circumference, with the addition 
of only a few series of vessels. As there is no true medullary 
cellular tissue in the axis, so there are no medullary rays passing 
through the woody cylinder ; it is however penetrated by the 
vascular bundles which supply the leaves which have been 
mistaken for or misnamed medullary rays. The woody cy- 
linder 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 layers. The inner zone has never, 
as far as I know, been perfectly preserved in any specimen, yet 
traces of it may be occasionally seen. Its absence arises from 
its extremely delicate structure. The cells of the middle zone 
have thicker walls, and have consequently more frequently 
resisted decomposition before fossilisation made them permanent. 
In the outer zone the cells are very much lengthened, and have 
a smaller diameter, resembling very closely true woody fibre. 
The cell walls of the three zones are without markings of any 
kind. 
The vascular bundles which pass through the woody cylinder 
traverse these cellular layers to the leaves and branches. Each 
bundle consists of scalariform vessels very much finer than those 
of the wood of the stem, surrounded by elongated cells like 
those of the outer zone, and probably still further by a delicate 
parenchyma, which disappeared before it was fossilised. The 
only evidence I have of the existence of this cellular tissue is 
that the bundles never fill the cavities in the tissues of the stem 
through which they pass. The vascular bundles terminate in 
the points seen on the areoles of the stem, which are the scars 
of the bases of the leaves. 
The woody cylinder is of different thicknesses in different 
stems, and appears to have increased with the growth of the 
tree; there is however no indication of interruption in the 
growth or of seasonal layers ; but the whole cylinder could not 
have been developed at the same time. It is very probable 
that the zone of slender and consequently rarely preserved 
cellular tissue which surrounded the woody cylinder was analo- 
gous in its functions to the cambium layer of phanerogamous 
stems, like a similar structure which occurs in recent Lyco- 
podiaceoe. 
The leaves were simple, lanceolate, acute and sessile. They 
had a single median nerve. The younger branches were 
