COMPARATIVE ANATOMY OF THE CYCADACER. 449 
In the stalk common to the two united cotyledons there are 
four small bundles in the normal row of each half, mostly entirely 
concentric (fig. 14), and one much larger bundle, collateral in 
structure and normally orientated, situated towards the inner 
side of each half. 
This large inner bundle has well-developed xylem and phloem 
in the normal position. On its inner side there are several irre- 
gular divisions in the cells bordering on the xylem. Higher up in 
the cotyledon, but still in its basal part, the large inner bundle 
has a little phloem on the ventral side of the xylem, but the 
phloem here appears to be dying out all round. 
In the upper part of the stalk of the cotyledon, where it has 
become a distinct and separate organ, the tracheides of the inner 
bundle become large and more or less isodiametric; divisions 
representing phloem occur on both sides or all round the xylem, 
the latter case constituting it a concentric structure; the divisions 
on the ventral side are much more definite and regular. Proto- 
xylem is not here easy to distinguish, though in one case one or 
two small elements are seen adjoining the most definite divisions. 
Still lower down in the stalk the tracheides are seen to run out 
away from the bundle in a tangential direction, and are here 
large, isodiametric, and angular. They eventually, lower down, 
as shown by the succeeding sections, entirely vanish. The phloem 
also disappears. The small normal bundles of the cotyledon, 
in the lower part of the stalk, lose their complete concentric 
structure (fig. 16). 
Periderm arises allround the stalk of the cotyledon, cutting 
off the outer few layers of cells. 
In the lamina of the cotyledon bordering on the crushed 
endosperm-layer, is a very conspicuous absorptive layer. Tts cells 
have thick walls, dense protoplasmic contents, and conspicuous 
nuclei. 
I consider it highly probable that the primary concentric bundles 
of the cotyledon of this plant, like the primary concentric strands 
in the peduncle of the mature plant*, are relics of a structure 
which was once, probably, a common feature of the ancestors of 
the Cycadacem, the concentric very frequently replacing the 
collateral arrangement of the vascular strands in those days. As 
an instance amongst fossil plants which I believe to be nearly 
* D. H. Scott: “The Anatomical Characters presented by the P eduncle of 
Cycadaceæ,” Ann, Bot. vol. xi. 1897. 
