82 DR. D. H. SCOTT ON THE HETERANGIUMS 
In this specimen the arrangement was evidently the same, in essentials, as 
in specimen 1, the leaf-trace being double, with widely separated strands 
and roots between them. 
Specimen 3 is a little different. In one section (S. 446) the bundles of the 
one pair shown are only about 0*8 mm. apart ; the preservation of the outer 
tissues is, however, so bad that one eannot be certain that the interval is 
natural. In a better-preserved section, probably of the same stem (W. 1915 P), 
two bundles are shown well out in the pericycle and 1:6 mm. apart ; each 
shows signs of division. There is no certain evidence for a second trace in 
any of the sections. [t is evident that this specimen really agrees with the 
previous two ; if the strands of a trace are sometimes nearer together, this 
may well be due to the absence of adventitious roots between them. 
Specimen 4 is of the same type. A pair of bundles lies in the pericycle, 
1:64 mm. apart (in R. 645). Between them a root passing out horizontally 
is beautifully shown. The stem is a comparatively young one ; the secondary 
wood is considerably thicker on the side where the trace and root are, but 
there is not yet any excessive hypertrophy such as one finds in older stems. 
Specimen 5, already referred to for the good preservation of the phloem 
and the absence of Sparganum structure, is peculiar in the character of the 
leaf-traces. In the section photographed (S. 625; Pl. 2. Phot. 13) two traces 
are shown, each consisting of two bundles. The inner trace (T. 1) is passing 
out through the secondary wood; in this position each strand has its own 
secondary arc. The primary xylem-groups are about 1:6 mm. apart, and are 
unusually small, about 300 u and 240 u respectively in tangential diameter, 
about half the diameter of those in the smaller stems previously considered. 
The primary tracheides are also small—only the outer part of the stelar 
strands appears to have contributed to the trace-bundles. This trace is of 
interest, for it is the first one we have met with in the act of leaving the 
wood, and it shows that the bundles were well separated at their first origin 
from the stele. 
The outer trace (T. 2, almost opposite the former) is in the pericycle. It 
consists of two small strands (about 220 u in diameter) about 1 mm. apart. 
They have no secondary wood. In the next section (R. 639), which appears 
to have been eut about 7 or 8 mm. lower down the stem *, the inner trace has 
disappeared, having completely fused with the stele. The outer trace is still 
in the pericycle, the bundles here are larger (about 320 p) and only about 
0:75 mm. apart. They are fully as large as those of the inner trace; so we 
must assume that these two bundles represent an entire leaf-trace and not 
the product of any subdivision. The distance between the strands of a pair 
is evidently a very inconstant feature. In this specimen several adventitious 
* This is roughly calculated from the dimensions of a 7rigonocarpus seen in transverse 
section in both slides. 
