446 MR. W. C. WORSDELL ON THE 
the bundle; the outermost tracheides are larger and have 
reticulations on their transverse walls, some of the latter being 
interspersed amongst the ordinary tracheides of the centripetal 
xylem. Thus the same transition occurs here between the 
centripetal xylem and the transfusion-tissue as is the case iu 
Cycas. 
The bundles of the petiole of the young foliage-leaf have the 
normal Cycadean structure, the xylem consisting, in the upper 
part of the organ, chiefly of centripetal, in the basal part almost 
entirely of centrifugal xylem. An interesting transition between 
these two types of xylem-development can be followed where, in 
proportion as the centripetal xylem decreases, the centrifugal 
xylem increases in quantity, until the latter completely replaces 
the former. 
A transverse section of a thick scale, situated in the region 
between the insertion of the cotyledon and that of the foliage- 
leaves, shows it to possess three bundles with mesarch structure 
and four or five mucilage-canals ; in each of the latter is a fringe 
of thyloses, these not having extended as far as the centre. On 
the dorsal side of the scale are two distinct layers of periderm, 
which become confluent towards the margin. 
The stem exhibits a single cylinder of vascular tissue. The 
xylem-strands, as usual in Cycads, have a very irregular, curved 
course. Reticulate protoxylem-elements occur on the inner side 
of the wood. 
As showing what marked and important variation in structure 
may occur between two species of the same genus in this order, 
I may recall the structure of the stem of Macrozamia Fraser, 
Miq., in which, besides the first-formed cylinder, two or three 
others arise successively ou its outer side; while 1n the p y 
well-developed cauline system of bundles is present . m 
M. spiralis, Miq., neither of these highly interesting characters 
in the structure obtain. It is true that 1 am describing Very 
young plants of this species; but I feel sure that they are none 
young but that, if these characters were really possessed VÀ ir 
plant, they would already have gıven some indication of the 
presence. 
In a transverse section of the hypocotyl, where the ce . 
cylinder is stil of considerable thickness, strands of ‘he 
cular tissue are seen passing obliquely outward from 
ntral 
* Worsdell, Ann. Bot. vol. x. 1896. 
