Affinities of Sutcliffia . 
1045 
height is considerable. The principal rays extend from the parenchyma of 
the primary wood to the external limits of the secondary phloem, but shorter 
secondary rays may arise in the secondary wood. In some places the 
secondary xylem may be locally very parenchymatous in nature, the 
tracheide rows or files being 1-2 cells thick, while the medullary rays are 
5-6 elements in breadth. The rays are made up of thin-walled parenchyma 
cells, in which the longest diameter lies in the radial direction. 
The tracheides of the secondary wood are of the same multiseriate type 
as those of the primary xylem, though they are arranged with much greater 
regularity; their average diameter is distinctly smaller, being only 159 /x. 
The diameter of the first-formed secondary tracheides is much less than that 
of the later formed ones, 
being only from 33 to A 
67 ju, the full size of the 
elements beingonly grad- 
ually attained (Text-fig. 
12, and PL XCI, Fig. 1). 
Owing to the kind- 
ness of Dr. Scott, I had 
the opportunity of ex- 
amining a section of Sut- 
cliffia insignis in which 
secondary growth was 
just beginning, and it 
is of great interest to 
note that the size of 
the secondary tracheides 
which are there forming 
agrees exactly with the 
similar elements in the 
new stem. 1 
No trace of cambium could be distinguished, but the preservation was 
not perhaps sufficiently good to warrant such an expectation. 
It frequently happens that the continuity of the secondary wood is 
interrupted, the radial seriation of the elements starting afresh at a certain 
distance outwards, so that the new series no longer corresponds with the 
cells previously formed ; the size of the elements after the break is always 
considerably smaller than before. At these places there is produced 
a superficial resemblance to an annual ring, but that it is merely superficial 
is clear from the fact that the phenomenon is purely local, and never ex- 
tends completely round the stele ; it is evidently due to some local irregu- 
larity in cambial activity (PI. XCI, Fig. 1). It is interesting to note that 
1 Cf. Scott, Sutcliffia insignis } Plate VIII, Fig. 10. 
Text-fig. 12. Transverse section of part of the wood of 
the stele, showing the small size of the first-formed secondary 
elements, x 70. p.xy = protoxylem ; x 1 — primary xylem ; 
x 2 = secondary tracheides ; m.r. — medullary ray ; x.p. xylem 
parenchyma. 
