606 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
in fig. 3. The meristematic tissue is composed of small cells filled with dense 
contents, which evidently represent the slightly contracted protoplasts. The elon- 
gation of the cells in the central region of the stem is apparent a short distance 
behind the actual apex. The cells of the growing point itself are isodiametric, and 
those of the outermost layers were evidently undergoing periclinal divisions. The 
whole appearance suggests a small celled meristem, but it is of course impossible to 
say whether an apical cell was present or not. The cuticle can be traced from the 
older contracted region of the branch over the growing point ; it has become separated 
from the outermost layer of cells by a clear zone. 
By the side of this undoubted apex, at b in fig. 2, is seen what we can only 
interpret as the extreme tip of another growing point which has been removed by a 
horizontal section and is thus viewed from above. The arrangement of the meri- 
stematic cells in this transverse section is shown more highly magnified in fig. 4. 
If this interpretation is correct, the specimen gives additional evidence as to the 
absence of any prominent initial cell. 
In connection with the apical meristem, fig. 5 may be referred to. This longi- 
tudinal section, while not including the apex, shows a region situated close to it with 
the protoplasts almost filling the small cell cavities. 
The only sporangium of R. Givynne-Vaughani figured in Part I (PI. IX, figs. 
63, 63a) lay amongst characteristic stems of that species, and terminated a stem 
showing the distinctive vascular strand and tracheides. It contrasted with what 
we now know to be the sporangia of R. major by its much smaller size. It measured 
about 3 mm. in length by 1 mm. across. At the junction of stalk and sporangium 
in this specimen there is a constriction (PI. I, fig. 6) to which we do not attach 
importance as indicating a natural feature. Above the constriction the epidermal 
cells assume the character of the sporangial wall. They are deeper than on the 
vegetative stem, but as seen in surface view at the top of the sporangium have the 
fusiform outline (PI. I, fig. 7). The cell walls are moderately thickened and brown. 
Within the well-marked epidermis come some layers of thin- walled tissue, mostly 
perished, and only indicated towards the base of this sporangium. Bounding the 
empty cavity of the sporangium is the persistent layer which we have spoken of 
in Part I as the “ tapetum.” The nature of this layer in the sporangia of Rhynia 
will be further considered below under R. major. 
A transverse section of a slightly larger sporangium is shown in fig. 8. The 
well-developed epidermal layer, the perished middle zone of the sporangial wall, and 
the persistent tapetal layer can be distinguished. The sporangial wall is about '2 mm. 
in thickness, and the width of the sporangium must have been slightly over 1'5 mm. 
There were no spores remaining in this sporangium, but another of similar size, and 
with an equally well differentiated wall (fig. 9), was filled with well-preserved spores. 
The tapetal layer in this specimen appears a number of cells deep, but this is probably 
to be explained by the section being oblique. 
