Kershaw.—A Fossil Solenostelic Fern. 685 
Anatomy . The general view of the stem is seen in Fig. 1, 
PI. LVIII. Unfortunately in most of the sections the greater part of the 
cortical ground tissue has disappeared, so it is impossible to determine 
the size of the complete stem. The stele measured about i*8 mm. 
diameter. 
Ground tissue. The central ground tissue (within the solenostele) is 
composed of cells 0-05 mm. diameter, with sclerized walls. As may be seen 
from Fig. 1 at c.scl. , the central cells are larger and less sclerized than the 
peripheral ones. These larger central cells are often filled with rounded 
bodies which were probably starch grains, such as are found in similar cells 
in living ferns, e. g. Microlepia. 
Almost at the edge of the central ground tissue, separated only by one 
or two layers of sclerenchyma from the solenostele, is a layer of rather 
irregular, thin-walled cells, which in many parts are very crushed in the 
fossil (Figs. 1 and 2, s.). A similar layer of thin-walled cells amongst the 
sclerized ones is frequently met with in the central ground tissue of the stem 
of living solenostelic ferns. 
The cortical ground tissue is not seen very favourably in many of the 
sections, and is in no case complete. Immediately surrounding the stele 
there is a layer of sclerenchyma about three cells in thickness (Figs. 2, 3, 4, 
0. sell). Many of these cells, as in the case of the cells of the central ground 
tissue, are filled with the rounded bodies referred to above as starch grains. 
In most of the sections the tissues outside this sclerized ring are lost, but in 
some of the retained portions there may be seen, outside the sclerized ring, 
several rows of parenchymatous cells usually rather crushed, but which were 
probably of a soft, spongy nature, and had large air spaces between them. 
This tissue can be seen as a dark ring just outside the sclerized cortical 
tissue in Fig. 4, i. c. 
The outer cortex, which was probably a much stronger tissue, is 
partially preserved in some of the sections—see Figs. 3 and 4, o. c. ; but 
in no case can the epidermal tissues be seen. The cells composing this 
outer cortex, usually hexagonal in shape and averaging 0-07 mm. diameter, 
fit together closely, leaving no intercellular spaces. 
The stele conforms to the definition of a solenostele given by Gwynne- 
Vaughan, 1 for ‘ the vascular tissue is arranged in a single hollow cylinder 
with phloem and phloeoterma on either side . . . the complete continuity of 
which is interrupted only by the departure of the leaf-traces; the gaps thus 
produced are closed up in the internode above, before the departure of the 
next leaf-trace ’. There is only one node and a portion of an internode 
in the fossil fragment, but those parts are in agreement with the above 
1 Gwynne-Vaughan (’ 01 ), Observations on the Anatomy of Solenostelic Ferns (Part I). Annals 
of Botany, vol. xiv, March, 1901. 
