COMPARATIVE ANATOMY OF THE CYCADAOER. 453 
of Cycas or Macrozamia. All the tracheides of the secondary 
wood have scalariform pits, this affording a marked distinction 
from the two genera just cited. The protoxylem is largely 
obliterated ; its remains are seen scattered among the pith-cells 
in the neighbourhood of the wood, some of the reticulate elements 
being still preserved in this region. There is a large amount of 
crushed phloem. The phloem does not attain such a relative 
thickness as is the case in Cycas or Macrozamia, being narrower 
than the xylem. It contains fibres. 
In the pith are numerous branching bundles. They are seen 
passing into the ring all round its circumference, and they run 
in various directions throagh the pith and branch considerably. 
Some of the branches can be traced along medullary rays, where 
they eventually unite with the vascular tissues of the cylinder. 
There can be little doubt that these bundles belong to a pedun- 
cular cylinder traversing the pith, a fuller explanation of which 
will be given when describing the next genus. 
The only anomaly presented by the stem of this plant is the 
peculiar strand of secondary tissue, composed of tracheides and 
parenchyma, which apparently traverses the phelloderm at the 
periphery of the cortex. It is highly probable that this tissue is 
avestige of some former system of cauline concentric vascular 
strands characteristic of the ancestors of this plant, and I consider 
it probably homologous with the cortical cauline strands of 
Cycas. 
CERATOZAMIA MEXICANA, Brongn. 
A large stem whose apex had been destroyed, and which was 
otherwise rendered unfit for further cultivation, was brought into 
the Laboratory from the Gardens, and placed at my disposal for 
investigation. It had a diameter of about 8 inches. This genus 
also belongs to the type possessing but a single vascular cylinder. 
€ stem, upon examination, was found to exhibit remarkably 
clearly the presence of the successive peduncular cylinders of 
vascular tissue in the pith, this being the only point of special 
interest in the whole structure. The tracheides of the outermost 
Part of the wood of the cylinder have transversely-elongated 
rdered pits on their radial walls ; those of the innermost part 
of the wood have scalariform pits. The protoxylem elements 
“ere not observed, having been destroyed during the growth and 
*Xpansion of the pith-cells. 
212 
