266 BOTANICAL GAZETTE [APRIL 
primitive structures are retained, as in so many former cases, only 
in the petiole and blade. The vascular anatomy of this portion of 
the plant, with special reference to the position of the protoxylem, 
was investigated by the writer in a considerable number of species. 
The results obtained agree in general with those of METTENtUS (4) 
and other later investigators. 
At the very base of the leaf trace in all the species the primary 
wood becomes increased in amount at the flanks of the bundle, 
and two adaxial projections are here formed which finally unite 
behind the original position of the protoxylem and inclose a small 
island of parenchyma. The protoxylem either follows one or both 
of these masses of metaxylem backward, always remaining attached 
to them, or else swings over to the centripetal wood as soon as 
the two arms of the latter unite. Just before this change takes 
place, the bundle presents a close similarity to that of the leaf of 
Prepinus, for both centripetal and centrifugal wood are well 
developed, and the protoxylem is in seriation with the latter 
(fig. 5). 
The centrifugal wood becomes very rapidly diminished in amount 
as the bundle ascends, so that in the middle and upper portion of 
the petiole in many species, such as Zamia integrifolia and Encepha- 
lartos Altensteinit, it is either absent in most of the strands or repre 
sented by only two or three elements (fig. 2). It is also noteworthy 
that, except perhaps at the very base of the petiole, this ou 
xylem seems to be entirely secondary, as is shown by its relation 
to the phloem. All but the extreme outer part of this latter — 
is clearly secondary and radially arranged, and the centrifugal 
tracheids are almost always just at the inner ends of the rows 
of phloem elements, and seem unquestionably to have been Pro 
duced by the same cambial activity (figs. 1 and 3). They 7 
usually pitted and not scalariform, as are most of the elements 0 
the centripetal xylem. 
* These include Cycas verticillata, C. media, C. celebica, C. ruminiana, C- OT 
cinalis, Zamia furfuracea, Z. macrophylla, Z. Loddegesii, Z. integrifolia, Z. Skinne™ 
Z. Linderi, Z. muricata, Z. Seiboldii, Ceratozamia latifolia, C. mexicana, C. kuestend™ 
Encephalartos horridus, E. Altensteinii, E. Lehmanii, Microzamia spiralis, Dioon 
edule, and Bowenia spectabilis. 
bar 
