664 DR R. KIDSTON AND PROF. W. H. LANG ON OLD RED SANDSTONE PLANTS 
The above general mental picture of the vegetative organs of Asteroxylon may 
be said to be established in its main features. The connection of the various parts 
as belonging to one plant is proved by direct evidence of continuity and by the 
histological identity of important tissues. 
On the other hand, conclusive evidence is wanting as to the fertile region and 
sporangia of Asteroxylon. On the ground of close association we regard it as prob- 
able that certain slender axes of peculiar structure and a type of dehiscent sporangia 
constituted the fertile region of this plant. Our knowledge of Rhynia Gwynne- 
Vaughani, Rhynia major, and Hornea Lignieri makes it certain that the structures 
in question have nothing to do with them ; they either belong to Asteroxylon or to 
an additional plant from the bed, of the existence of which there is no further 
evidence. The weight we are prepared to lay on the peculiarly close association is 
indicated by not giving separate names to these peculiar axes and sporangia. It 
must be left for future investigation to confirm the assumed connection of these 
structures with Asteroxylon, or to show that they belong to another plant. 
Even if our assumption is correct, we have no evidence as to the mode of connec- 
tion of the peculiar fertile axes and sporangia with the vegetative shoots. The 
fertile axes might have replaced the leaves on a distal region of the shoot, or have 
been ultimate subdivisions of a fertile region continuing certain vegetative shoots. 
If we assume that these parts were the fertile region of Asteroxylon, we can 
vaguely complete the picture of the plant, with the leafless rhizomes and branched 
leafy shoots, by fine branched leafless axes bearing dehiscent sporangia. The 
morphology and habit of the vegetative region of Asteroxylon are practically estab- 
lished by evidence. The suggestions as to the fertile region are, at most, probable. 
Diagnosis and Classification. 
Asteroxylon, Kidston and Lang, n.g. 
Diagnosis. — Plant consisting of leafless rhizomes continuing into branched aerial 
stems bearing numerous small leaves. Stele of rhizome with a cylindrical strand of 
xylem, while the xylem of the stem-stele is stellate and gives off leaf-traces. The 
fertile region probably consisted of slender, branched, leafless axes bearing pear-shaped 
sporangia of moderate size, with definite dehiscence at the wider jfree end. 
Asteroxylon Mackiei, Kidston and Lang, n.sp. 
Diagnosis. — Khizomes from over 5 mm. to under 1 mm. in diameter, some of the 
branches evidently behaving physiologically as roots ; no absorbent hairs ; epidermis, 
outer cortex and inner cortex ; stele with zone of phloem around a central strand of 
xylem. 
Transition region from rhizomes to shoots, with stomata in the epidermis and 
