224 WorsdelL — The Vascular Structure of 
form an almost concentric structure (Fig. 18); indeed, in 
another species, E. horridus , Lehm., a primitive concentric 
structure for these bundles appears to be indicated by the 
peculiarity presented by some of them, as, for instance, one 
bundle which is curved into a horse-shoe shape so that the 
xylem from opposite sides almost meets at the open part 
of the strand so as to enclose a pith with protoxylem round 
its periphery ; in another larger, tangentially-elongated strand 
which is but slightly curved, there occur on the ventral side 
of two groups of centripetal xylem, and intimately connected 
therewith by radial rows of cells, two distinct groups of 
crushed phloem-cells, with a slight indication of these latter 
having at one time been united by similar tissue ; thus the 
combination of this phloem with the groups of centripetal 
xylem affords the phenomenon of two small strands with 
inverted orientation on the ventral side of the main strand ; 
other groups of centripetal xylem occur belonging to the 
same strand, but isolated and without any sign of phloem near 
them (Fig. 19). 
In the lamina the strands have about the same general 
structure ; but here the centrifugal xylem is extremely 
reduced as compared with that in the stalk, its tracheides 
also being usually much smaller ; it is about equal in de- 
velopment to the centripetal which occurs in considerable 
quantity, and in some bundles extends as transfusion-tissue, 
with scalariform thickenings on the transverse walls of the 
tracheides, both laterally, and even quite on to the dorsal 
side of the phloem. In E. horridus , Lehm., protoxylem was 
only seen on the side of the centripetal xylem. 
The megasporangium receives 4-5 bundles, some of which 
have a very distinct concentric structure (Fig. 20). 
Macrozamia Fraseri, Miq. 
Male Sporophyll. There are about a dozen bundles in the 
stalk lying in a regular row and somewhat unequal in size. 
They all have sharply-defined and brightly-stained centri- 
