380 Watson . — On Mesostrobus , a New Genus of 
It is succeeded by a zone of parenchyma, seven or eight cells wide, 
which is composed of isodiametric cells about 0-015 mm. in diameter ; this 
belt is the zone, called by Bower, Weiss, and myself the inner cortex ; it has 
a definite termination outwardly, and is succeeded by the middle cortex. 
This forms a zone about 0-16 mm. in breadth (Phot. 3 and 4). It is com- 
posed of isodiametric cells about 0-05 mm. in diameter, which have large air 
spaces between them. It is not very well preserved, but this is, I believe, 
the first Lepidodendroid cone, except Lepidostrobus Brownii, in which it has 
been at all fit for description. It resembles exactly the middle cortex of 
any small Lepidodendroid twig, and bears a particularly close resemblance 
to that of an undescribed Lepidostrobus , of which I possess sections. 
The middle cortex changes suddenly into the outer cortex (Phot. 3). 
This latter consists of a parenchymatous tissue which is strengthened by 
a sclerized 1 skeleton. The parenchymatous foundation is composed of 
cells which are isodiametric in transverse section, and about 0-04 mm. in 
diameter ; so far as can be seen from transverse sections, the sclerized 
portions are composed of cells of exactly similar size and shape. 
The sclerized skeleton is associated with the insertion of the sporophylls, 
and is arranged roughly as follows (Phot. 1) : — 
At the lowest point, where the sporophyll-trace is just emerging from 
the inner cortex, it forms, as seen in transverse section, a small patch on the 
inner side of the outer cortex. Followed upwards this patch enlarges 
radially until, where the leaf-trace begins to turn out from the middle cortex 
to the outer cortex, it forms a somewhat narrow plate extending radially 
across the entire outer cortex. This gradually broadens tangentially until 
it is the entire width of the base of the sporophyll. In this region the trace 
passes out through a non-sclerized passage in the sclerized tissue. Above 
the insertion of the sporophyll the sclerized patch gradually contracts, 
appearing last at the outer edge of the cortex. It is very hard to be sure 
of the exact details of the arrangement of this skeleton owing to lack of 
sufficient sections, and to the fact that it is probably liable to considerable 
individual variation in detail. The foregoing account is, I believe, in the 
main correct. These patches obviously serve to afford a firm attachment 
for the sporophyll. 
The sporophylls are probably inserted on the stem in a series of spirals, 
they are at any rate not in whorls. 
They are composed of a more or less horizontal portion, and a vertical 
lamina on the surface of the cone. The horizontal portion is triangular in 
tangential section (Phot. 5), the upper surface being flat and the under side 
provided with a fairly sharp keel. The upper portion is of considerable 
breadth, measuring at its attachment to the axis as much as i*2 mm. across, 
1 This word is used throughout in a purely descriptive sense. 
