Shaw . — The Seedling Structure of Araucaria Bidwillii. 325 
In the other seedling, the bundles ( c.b .) from the cotyledons entered the 
plumular ring in pairs in such a way that the individual bundles of a pair 
form the ‘ horns ’ of different segments, which, as in the first case, are 
curved with the concavity outwards (Diagram III, Figs. 4, 5). When, 
therefore, the segments divide to form the paired bundles in the hypocotyl, 
each pair is identical with a pair of cotyledonary bundles (Diagram III, 
Fig. 6). 
Thus in both these cases there is evidence that each pair of bundles 
in the hypocotyl is identical either with a pair of bundles in the cotyle- 
donary tube or with a group of bundles which fuse to form an arc-shaped 
strand. 
The bundles in the hypocotyl pass down, remaining practically un- 
changed, through 2-3 cm. of the hypocotyl, which is extremely swollen 
and filled with starch. About the middle of the swollen hypocotyl a change 
takes place in each bundle. The primary xylem (p-x\) , which is practically 
identical with the protoxylem, begins to become separated from the 
secondary xylem (#.), and follows the course of the bundle at some little dis- 
tance from the inner face of the latter (Diagram II, Fig. 6 ; PI. XXI, Fig. 2). 
A longitudinal section shows the annular and reticulate elements of the 
protoxylem separated from the parent bundle by two or three layers of 
parenchyma. A little lower down, the primary xylems of any two bundles, 
forming a pair, can be seen curving towards a point midway between the 
respective bundles ; ultimately they fuse and form a single protoxylem group 
(PI. XXI, Fig. 3). Thus at the base of the hypocotyl there are half as many 
separate and distinct primary xylem groups as there are bundles, each 
group being situated between the two bundles with which at a higher level 
it was associated (Diagram II, Fig. 7). 
There are, therefore, five, six, or seven protoxylems, and these alternate 
with twice as many bundles consisting only of secondary xylem (x.) and 
phloem (A), and thus the structure is essentially that of a pentarch, hexarch, 
or heptarch root, in which secondary thickening has already taken place. 
As the hypocotyl decreases in diameter, the separate bundles of secondary 
xylem and phloem fuse to form continuous tangential bands between the 
primary xylem groups (Diagram II, Fig. 8) ; it should be noticed that this 
union is between bundles originally belonging to separate pairs at a higher 
level. The numbers of seedlings showing heptarch, hexarch, or pentarch 
structure respectively, 'were about equal. 
The further changes in the vascular system of the root will be described 
in a specimen which showed pentarch structure in the base of the hypocotyl, 
though the following remarks, mutatis mutandis , would apply equally to 
those with hexarch or heptarch structure. 
As a rule, the pentarch structure persists for some distance, running 
through the rapidly narrowing hypocotyl and into the main root ; its extent 
