608 Worsdell. — A natomy of Stem of Macrozamia 
from the vertical strands of wood owing to its obliteration by 
the expanding parenchyma of the pith. It is only where the 
xylem of a leaf-trace is curving outwards, as a broad band 
of tracheides, that the typical spiral and reticulate elements 
are preserved ; as they are in this position, perhaps, somewhat 
better protected against tension than elsewhere, though 
even here they are mostly isolated and broken up into 
fragments. 
On the interior vertical face of the wood, where the proto- 
xylem would naturally be sought, are often to be found the 
peculiar, irregular tracheides, resembling transfusion-tissue, 
above described as accompanying the medullary bundles. 
The tracheides composing the secondary wood have the 
normal bordered pits on the radial walls. On the tangential 
walls very minute simple pittings were frequently observed. 
Here and there, between the tracheides, are rows, usually 
one cell in thickness, of parenchyma, but there is only 
a comparatively small quantity of this present in the wood. 
A characteristic feature of the radial section of the wood 
is the large number of out-bending strands of tracheides 
which, passing through the medullary rays, are continuous 
with the girdle leaf-traces of the cortex. 
In a radial section of the phloem the greatly-elongated 
fibres are the most prominent objects. They serve, doubt- 
less, to add strength and durability to a stem so largely 
built up of parenchymatous tissues. Side by side with these 
are seen the sieve-tubes, much elongated elements on whose 
obliquely-extended terminal and lateral walls very numerous 
sieve-plates of diverse shapes are seen, even without any 
staining. No callus, however, could be detected after 
repeated attempts at staining with aniline-blue. This was 
also the result of Strasburger’s 1 investigation in the case 
of Cycas . who states that the cambial activity having ceased 
in this vascular ring, the sieve-tubes have lost their function, 
and therefore no longer deposit callus on their plates. But 
1 Loc. cit., p. 154. 
