836 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
stem certain of the cortical cells at two or three regions of the transverse section 
are markedly enlarged as compared with the others that are of normal size. A 
similar appearance was recorded for a stem of R. Gwynne-Vaughani in Part 1 
(p. 770, fig. 74). 
This feature, like the wound-reactions, suggests comparison with a reaction of the 
living plant to some prolonged stimulation. 
Hornea Lignieri (PI. II, fig. 3). 
For this plant also we have only the fragmentary remains of all the parts and no 
specimens to show the general habit or height. It has been represented as some- 
what smaller than Rhynia Gwynne-Vaughani since its stems did not, on the whole, 
attain the diameter of those of the latter plant, and also give the impression of 
having been less rigid. 
The reconstruction shows the tuberous lobes of the rhizome from which the erect 
stems arise. These were repeatedly branched dichotomously. Some of the finer 
branches terminate in the sporangia, which were considerably smaller than those of 
Rhynia Gwynne-Vaughani. The sporangia may stand singly or in pairs, or may 
themselves be actually involved in the dichotomy of the branch-apex which has 
produced them, and therefore appear lobed. 
We have no further facts to add to the description of Hornea given in Part II. 
Asteroxylon Mackiei (PI. II, fig. 4). 
Since Asteroxylon was a much more complex plant than Rhynia or Hornea, the 
reconstruction of its general external appearance from the fragmentary remains is 
more difficult, although there is evidence for most of the parts represented in the 
reconstruction. It has, however, been found necessary to infer the relative pro- 
portions and connection of the parts in forming a representation of the whole plant. 
Mention may first be made of features regarding which evidence will be found 
in the description of Asteroxylon in Part III. The existence of a dichotomously 
branched, leafless rhizome without absorbent hairs was fully established. Certain finer 
root-like branches of this were found to penetrate fragments of plants in the peat. 
A gradual passage from the leafless rhizome into the stem, which became clothed with 
small simple leaves, was also demonstrated ; in the intermediate, transition region the 
leaves make their appea'rance as small scales. The occasional, dichotomous branching 
of large leafy shoots was met with, but this contrasted with the predominantly 
lateral relation of the branches on most main axes. In the case of the lateral 
branches and the finer ramification of the plant, dichotomous branching appeared to 
be more probable. The leaves on the main stems and branches were closely crowded 
and attained a length of over 5 mm. The shoot must have had much the same 
appearance as that of various species of Lycopodium. 
