635 
Ovule of Bowenia spectabilis. 
of large parenchymatous cells containing starch. The innermost cells are 
completely filled with large starch grains, while in the cells further out the 
number and size of the starch grains gradually diminish. Those near the 
epidermis contain only a few small grains. Amongst the outermost cells of 
this layer there are scattered tannin sacs, which begin to form in a single 
cell ; then frequently an aggregation of such cells leads to the formation of 
one large sac. Deeper seated in this layer is a ring of large mucilage ducts, 
about i*5 mm. in diameter. The main ducts are vertically placed, and from 
them there are branches and anastomoses in a lateral direction. The outer 
series of vascular bundles lie among the innermost cells of this layer, 
separated from the stone layer by about two rows of cells. 
The bundles of this series are collateral and have a large amount 
of centripetal xylem (Fig. io, PI. LXI). The centrifugal xylem consists of 
fairly regular rows of tracheides proceeding from the protoxylem ; the 
phloem elements follow on in equally regular rows towards the outside, 
where there are a few crushed protophloem elements. The centripetal 
xylem is about equal in amount to the centrifugal, but the elements are 
rather larger in size. They lead directly from the protoxylem, and the 
elements spread towards the inner part of the integument. There is 
a definite sheath of parenchymatous cells surrounding the bundle. This 
structure is similar to that described in Encephalartos by Stopes, 1 and 
is a much simpler type of bundle than that which is described by the same 
author in some species of Cycas. 
The stone layer, which is yet only partially sclerized, extends from the 
base of the ovule, where it stretches completely across (Text-fig. 13), 2 and is 
penetrated by the inner series of vascular bundles, to about half-way up the 
micropylar beak. It is of almost uniform thickness, 0-3 mm., except in the 
basal region, where there is a slight increase. There is no indication of a diffe- 
rentiation of the stone layer into distinct parts as is the case in many Cycads. 3 
The tissue consists of cells slightly elongated vertically, which in the basal 
region interlace with each other, forming what would be a very resistent 
tissue when the cell-wall had hardened. Sclerification has as yet only taken 
place in the micropylar region and about half-way down the free part of the 
integument (Fig. 11, PI. LXI). The process apparently begins in the inner- 
most cells of the layer, which have very thick walls with slit-like pits, and 
gradually spreads outwards. There is a sharp line of demarcation between the 
outermost sclerized cells and the adjoining cells of the outer flesh, which con- 
tain starch. An interesting feature of the micropylar region of the ovule is 
the occurrence of a second ring of sclerized cells almost bordering on the 
micropylar tube and extending up about half its length (Fig. 11, PI. LXI). 
1 Stopes, loc. cit. 
2 Cf. Dioon , where there is a gap in the basal region of the stone layer. 
3 Dioon — Chamberlain, loc. cit. Cycas Beddomii — Stopes, loc. cit. 
