PRESENT POSITION OF PALEOZOIC BOTANY—SCOTT. 393 
the growth of our knowledge, but rather to attempt a concise state- 
ment of the present position of the question. I will begin with the 
Lyginodendree, the type member of which, Lyginodendron Old- 
hamium, has now been investigated in all its parts. 
LYGINODENDREA, 
The stem of Lyginodendron Oldhamium presents a structure in 
which, at first sight, Cycadean characters appear to predominate. 
(Pl. I.) There is a pith of considerable size surrounded by a zone 
of wood and bast, with a layer of cambium, sometimes perfectly pre- 
served, between the two; the greater part of both wood and phloem 
shows a regular radial seriation of the elements, and is clearly of 
secondary origin, the structure resembling that of the corresponding 
tissues in a recent Cycad. Around the pith, however, several distinct 
strands of primary wood are evident, a character not met with in the 
vegetative stem of Cycads. 
The primary xylem-strands belong to the leaf-trace system of the 
plant; they pass out through the zone of secondary wood into the 
pericycle, which they traverse for some distance, here, of course, 
assuming the character of complete collateral bundles. During its 
passage through the pericycle each leaf trace divides into two. The 
leaf-trace bundles of Lyginodendron have precisely the structure of 
the foliar bundles of recent Cycads, for their xylem is of the mesarch 
type, the centripetal portion exceeding the centrifugal in amount. 
The occurrence of this structure in the stem of Lyginodendron sug- 
gested a search for mesarch bundles in axial organs of Cycadacex, 
and they were found to occur in the peduncles of the cones of Stan- 
geria and some other genera. It may be pointed out that the tra- 
cheides of Lyginodendron, like those of almost all Pteridosperms 
investigated, are characterized by multiseriate bordered pits. On 
pl. 1 is shown the general structure of the stem, which need not be 
described in further detail. 
In its usual mature condition the structure is thus, on the whole, of 
a Cycadean type; in the fortunate cases, however, where a young 
stem, before secondary growth had begun, has come under observa- 
tion, the resemblance to the stem of an Osmundaceous Fern is very 
striking. 
When we come to the foliage we find that Fern characters alto- 
gether predominate. The petioles have often been found in connec- 
tion with the stem, on which they are usually arranged in a 2/5 
phyllotaxis. The foliar bundles, on entering the petiole, become 
more or less fused, and assume a concentric structure, which they 
maintain throughout the rachis, becoming collateral again in the 
leaflets. The highiy compound foliage has long been recognized as 
