COMPARATIVE ANATOMY OF THE CYCADACER. 113 
unite with the central cylinder they are of very different sizes, some being very small, 
others very large. The latter result from the fusion of two or three in the cortex 
before they reach the cylinder. In some bundles all the secondary tracheides have 
scalariform pits, these latter passing gradually over into the reticulations of the 
protoxylem. In some bundles the latest-formed secondary tracheides have bordered pits, 
and there is a gradual transition between these and the scalariform tracheides further 
to the inside. The scalariform pittings prevail in the bundles of the leaf-base, while 
those on the upper part of the petiole have bordered pits on their tracheides. 
Lower down, near the transitional region between stem and root, or the primary node, 
the central cylinder develops a much thicker ring of vascular tissue, with a correspond- 
ingly smaller pith. The inner elements of the wood, including the protoxylem, become 
disjointed and scattered about the pith. 
Immediately outside the central cylinder three or four large, fan-shaped strands are seen. 
The first-formed innermost tracheides are reticulated and parenchymatous in shape, 
lying without any regular arrangement on the ventral side of the later-formed typically- 
Shaped tracheides, These strands, if followed upwards, are seen to gradually bend 
inwards and eventually to fuse with the central cylinder; one such which was followed 
was seen to separate off, just before it fused, a small concentric bundle which passed 
again to the outside of the ring. The strands taper considerably as they pass upwards 
and inwards. 
Still lower down the cortical strands increase somewhat in size, the largest assuming 
a semi-cylindrical shape and enclosing a half-pith in which are scattered, loosely and 
irregularly, the same short, reticulate tracheides, the first-formed woody elements of 
these strands. The secondary wood and phloem of the latter is massive. There are 
also smaller, less regularly-shaped strands, which are elongated tangentially and 
contorted, or round, oval, and fairly regular in outline. The latter, the smallest, often 
lie immediately on the outer edge of the others in a somewhat oblique position. 
The xylem of these smaller strands consists for the most part of the short, reticulate 
elements with, often, but very few of the typical secondary tracheides. The larger 
strands may be either completely concentric in structure, which is rather the rarer case. 
(Pl. 15. fig. 3), or they may be greatly curved while retaining still the collateral character ; 
or, again, they may exhibit, on their inner side, traces of a cambium with two or three 
secondary elements cut off, here and there. 
The strands may, however, instead of exhibiting a semi-cylindrical form, be completely 
flattened out. 
Lower down in the axis they completely die away. 
These cortical cauline strands are homologous in nature with the concentric strands 
constituting the outermost, and occasionally (see infra) one of the intermediate, rings of 
the stem of Cycas, as also with the concentric strands immediately outside the root-stele 
in the primary node of the seedling of Cycas. They are, indeed, the very same strands 
which I have met with and described in the same region of the axis of Encephalartos 
horridus, Lehm.*, and which I stated, in the paper below quoted, to be homologous with 
. .* “The Comparative Anatomy of certain Species of Encephalartos,” Trans. Linn. Soc. ser. II. Bot. vol. v. pt. 14, 
1900. 
