6 1 2 JVorsdell. — A natomy of Stem of Macrozamia 
bundle. It is worth noting that here and there in the space 
between an inverted and a normally orientated segment, several 
of the short, angular tracheides with bordered pits above 
described as occurring in conjunction with the medullary 
bundles and the xylem of the principal zone, were seen (Fig. 
io) ; the presence of these added to the remarkable re- 
semblance which the whole structure bore to the concentric 
cauline bundles in the cortex of Cycas, for here also these 
curious tracheides occur in the so-called pith. Where frag- 
ments of a third anomalous ring occur in the shape of a few 
scattered bundles, these may also be accompanied by a similar 
inverted bundle. 
This peculiar tertiary cambial formation in connexion with 
the anomalous zones of secondary thickening in the stem 
of this plant has not hitherto been observed in the stem of 
any other genus. I could myself find no trace of a similar 
structure in connexion with any of the anomalous rings of 
Cycas media , of which plant I examined a very large stem 
with about a dozen vascular zones. At the same time, 
I believe, from a comparison made between the two, that this 
structure is homologous with that of the concentric cauline 
‘ bundles ’ so well known to occur in the cortex of Cycas. 
These latter appeared, in the adult stem which I examined, 
as tangentially-extended zones, each of which had an orienta- 
tion, as regards its xylem and phloem, the reverse of that 
in the other, the central region being filled with the short 
tracheides already mentioned. 
This anomaly in Macrozamia I believe also to be similar 
in nature to, and homologous with, the well-known structure 
described by Gregg 1 in the roots of Cycas Seemanni. 
The tranverse section of the stem shows clearly the passage 
of the leaf-trace bundles through the broad medullary rays 
from the cortex, traversing the successive vascular rings, to 
the normal cylinder. They may have connexions during 
their course with segments of each of the rings, thus establishing 
1 Anomalous Thickening in the Roots of Cycas Seemanni , Ann. of Bot., 
Vol. i, 1887. 
