236 W or s dell. — The Vascular Structure of 
structure. Centrifugal xylem nearly always present, 
often in large quantity. Small inverted strands 
attached to dorsal side of bundles, as in Cycas. 
Macrozamia, $ : two to three bundles in lowest part of stalk, 
which rapidly divide up into larger number with usual 
endarch structure ; no centripetal xylem. 
? : one of the largest in order ; bundles have very 
well-developed centrifugal and well-marked quantity 
of centripetal xylem ; bundles resemble very much those 
in ¥ of Encephalartos. 
Zamia, $ : three to four bundles in stalk with rather irregular 
arrangement and orientation ; centripetal xylem some- 
times present ; some bundles are partially concentric in 
structure. 
Z. Loddigesii , Miq., ? : four bundles in stalk, of which two 
lateral are largest. All bundles have centripetal 
xylem, whose elements are often larger than those of 
centrifugal portion. 
Z . furfur acea, Ait. ; Z. latifolia , Lodd. ; Z. Fischeri , Miq., ? : 
the four bundles have no centripetal xylem. A small 
bundle, either concentric or collateral in structure, 
occurs on ventral side of row as a branch from one of 
normal bundles. 
Z. Leiboldii , Miq., ? : abnormal, bearing three sporangia ; in 
consequence, vascular system of stalk is concentrated 
on side on which two sporangia are borne. 
Ceratozamia latifolia , Miq., <3 : medullary bundles, either con- 
centric or collateral in structure, in axis of cone ; three 
bundles in stalk of sporophyll ; no centripetal xylem. 
C. mexicana , Brongn., $ : of three bundles in stalk, median 
one is much smaller than other two. 
$ : ring or double row of bundles in 
stalk, whose xylem is in all cases directed inwards ; 
these arise from division of two original bundles arising 
from cylinder of axis. Owing to young state of organ 
no difference in respective development exists. 
