1044 
de Frame. — On the Structure and 
i&Rg 
Thin-walled xylem parenchyma forms a continuous network among the 
primary tracheides ; its cells are elongated transversely parallel to the 
tracheide walls just as in Scott’s fossil (compare PI. XCI, Fig. 2, with 
PI. IX, Fig. 13, of Scott’s paper). On the whole the parenchyma is less 
abundant than in the latter stem, giving an appearance of somewhat greater 
c woodiness 5 to the new fossil. A very characteristic feature in S', insignis 
is the presence of numerous elements with dark contents scattered through- 
out the xylem parenchyma (Text-fig. 6 ) ; in the new stem these secretory 
elements are apparently absent except in the case of one ‘meristele' (Text- 
fig. 10), in which such elements occur. 
The xylem parenchyma is, in most places, very badly preserved, so 
that the apparent absence of secretory elements may be due to this cause. 
Here and there, however, in both transverse and longitudinal series, are 
elements of a lighter colour, some 
giving an appearance of vacuola- 
tion ; these may quite possibly 
represent the secretory cells, so 
abundantly present in the much 
better preserved wood paren- 
P chyma of X. insignis. 
The position of the proto- 
xylem is always exarch, and it 
is very common for the promi- 
^ nent protoxylem groups to run 
in pairs (Text-fig. 1 1*. Compare 
with Scott’s photograph, 1 PI. IX, 
Fig. 11). In longitudinal sections 
the protoxylem is seen to be 
composed of spirally thickened 
elements which are succeeded 
towards the inside of the stele or ‘ meristele ’ by denser spiral and then 
multiseriately pitted elements, the latter composing the bulk of the wood. 
In all the vascular strands the arrangement is similar (PI. XCI, Fig. 3). 
A characteristic feature of the fossil is the presence of a broad zone of 
secondary wood and bast, which entirely surrounds the primary wood in the 
main stele, and either entirely or partially encircles the ‘ meristeles ’. The 
thickness varies in the stele and ‘ meristeles ’ of different sizes ; in the former 
it may attain a breadth of 0-9 mm., but in the latter its dimensions are 
usually much smaller. The secondary tracheides are arranged in regular 
radial series, separated by medullary rays ; frequently one series of tracheides 
only lies between two rays, though as many as 3-5 may occur. The 
average breadth of the medullary rays is from 3 to 4 cells, but their vertical 
1 Scott : Sutcliffia insignis , loc. cit. 
Text-fig. i i . Transverse section of part of the 
primary xylem of a meristele, showing the 1 paired ’ 
protoxylem groups. x 70. p.xy. = protoxylem ; 
x 1 = primary xylem. 
