328 Shaw . — The Seedling Structure of Araucaria Bidwillii. 
curve away from one another and attach themselves to the inner side of the 
secondary xylem (Diagram V, Figs. 1 and 2 ). At this stage, therefore, the 
root contains an outer ring of vascular tissue with normal endarch proto- 
xylem and an inner ring with inverted orientation. 
A gap now appears in the outer ring, and its cambium becomes 
continuous with that of the inner round the edges of the gap, the inverted 
xylem also becoming continuous with the normal (Diagram V, Fig. 2 ). 
In this way a stele is formed consisting of a U-shaped mass of xylem 
enclosing a pith and surrounded by phloem (Diagram V, Fig. 3). Lower 
down in the root, the stele tends to straighten out, and it finally splits 
in a plane at right angles to its greatest breadth. The two segments 
immediately close up, each forming a single concentric stele, one of which 
gives off a small strand (/.) ending blindly in the parenchyma at a lower 
level (Diagram V, Fig. 4). 
Both of the steles now divide in a plane at right angles to the first 
division, and thus give rise to four steles in the root (Diagram VI, Fig. 5). 
Of these four steles, one (A) appears to die away at a lower level, while the 
other three go through a complicated series of changes to form the diarch 
