660 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
the clear peaty matrix. Adjoining the peculiar axis shown in fig. 103 the peat contains 
several more or less damaged specimens of sporangia still filled with the spores. 
The rhizome or rhizome-like axes in this peat call for a brief reference. Some 
of them are most naturally regarded as rhizomes of Asteroxylon, but others have 
suggested a different interpretation. It is possible that we have in this block aerial 
axes of Asteroxylon with a simple strand of xylem that are difficult to differentiate 
from the rhizomes. It is unnecessary to multiply examples of such structures, the 
nature of which must be left doubtful, but it seems desirable to record our impression 
of the problem for future elucidation. It would be misleading to dismiss all these 
remains as rhizomes, which they undoubtedly closely resemble, without raising this 
question. 
The association of the remains of Asteroxylon with the peculiar axes and sporangia 
is such as to suggest strongly the possibility of the latter constituting the fertile 
region of the same plant. We therefore describe them below, without giving them 
special names. It must, however, be clearly stated at the outset that we have not 
obtained evidence either of continuity or of histological identity which would con- 
vert the possibility or probability of their belonging to Asteroxylon into a certainty. 
The peculiar axes and the sporangia will now be described as the possible 
sporangiophores and sporangia of Asteroxylon. Their reference to this plant will be 
discussed later in the paper. 
(a) The 'peculiar Axes or possible Sporangiophores of Asteroxylon. 
The general appearance of these in the peat is well shown in figs. 102 and 105 on 
PL XV. The preservation is poor, the cortical tissues having usually disappeared, 
but the outline is often traceable by the more or less persistent epidermis, and the 
stele also persists. In the stele the xylem, composed of narrow elements, is often 
still surrounded by remains of the collapsed thin -walled tissue, which, from its posi- 
tion, will be referred to as the phloem. The decay and disappearance of the cortex 
render the outline of the longitudinal sections of these axes difficult to follow, but it 
is evident that they were of considerable length, and branched dichotomously. 
One of the specimens from the block in which they were first met with is shown 
in transverse section in fig. 107. The circular outline is only disturbed by contrac- 
tions during preservation. The epidermis and cortex are poorly preserved. Centrally 
placed, there is a paired stele with two groups of xylem enclosed in a common invest- 
ment of thin-walled phloem, which extends between them. The elements of both 
xylem and phloem are much narrower than in the undoubted vegetative organs 
of Asteroxylon. 
The arrangement of the tissues in the steles of these axes exhibits a remarkable 
variety, which is best seen in comparing the transverse sections. Some characteristic 
examples are represented in figs. 108-116. In the simplest case the stele was single, 
and consisted of a solid core of xylem surrounded by a zone of phloem (figs. 108 ; 
