216 DR. D. H. SCOTT : 
but shows the whole of the pith and primary wood; the preservation is 
remarkably good (Phots. 21 & 22). The pith is quite small, about 1°8 x 
1-4 mm. in diameter, including the primary wood. 
Around the pith there are six distinct primary xylem-strands ; in addition 
there is a seventh. strand entering the wood, and lying immediately outside 
one of the circum-medullary strands (Phot. 22). The latter stands rather 
further back in tbe pith than usual, but at this level is scarcely, if at all, 
separate from the outgoing strand. The pair presumably represents a leaf- 
trace with its reparatory strand. 
The first point that strikes one about the: primary xylem-strands, as 
compared with those of C. annularis, is that they are almost circular in 
section and centrally mesarch ; the protoxylem is in the middle of the strand ; 
the centrifugal portion is just as well developed as the centripetal, and has 
equally large elements (Phot. 22). This holds good without any qualification 
for five out of the seven strands; only in the strand entering the wood, and 
in a less degree in one other, also partly embedded in it, is there any 
reduction of the centrifugal primary xylem. In these two cases it may be to 
some extent merged in the secondary layers, as we found in the case of 
Archwopitys Eastmanii (Scott & Jeffrey, 1914, p. 347; Pl. 38. fig. 17). 
The predominance of centrally mesarch structure is a striking contrast to 
C. annularis and C. americana, and a striking point of agreement with 
C. fascicularis and C. Beinertiana, so far as the large xylem-strands of the 
latter two species are concerned, 
Another point about the xylem-strands in this specimen of C. Saturni is 
that they are quite well defined and to all appearance perfectly separate 
from one another. In no case (except of course that of the leaf-trace 
and its reparatory strand) have I found any sign of continuity between 
the bundles. The perfect preservation allows the tracheides with their 
somewhat thick and distinctly pitted walls to stand out quite clearly from 
the thin-walled parenchymatous cells* of the pith. In every case the 
xylem-strand forms a definite, more or less circular group of tracheides, while 
the whole of the tissue lying between the strands, whether the intervals 
be broad or narrow, is parenchymatous and identical with that of the pith 
(see Phot. 22; also Zalessky, 1911, Pl. 3. figs. 1, 2). The bundles are, in 
fact, just as distinct as in Lyginopteris or Porowylon ; there is no sign of a 
continuous xylem-ring. 
The whole of the pith appears to consist of thin-walled parenchyma. 
Every cell is preserved and I find no indication of medullary tracheides, 
except in one doubtful case, in the outer part of the pith. If present at 
all, the medullary tracheides must here have been in the last stage of 
reduction. 
* The wall (or middle lamella?) appears as a clear thin line with irregular deposits of a 
dark substance on either side. 
