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80 DR. D. H. SCOTT ON THE HETERANGIUMS 
that leaves and roots would be borne on the same side of the stem, and, as we 
shall see presently, adventitious roots come off in our specimen between the 
two leaf-trace bundles. 
It thus appears that the leaf-trace was a double one, with the two strands 
very far apart. 
The bundles are unusually large, the xylem of each measuring at least 
1*4 by 0-8 mim. ; each has a coneavity on the outer side and is intersected 
radially by a band of narrow elements (parenchyma ?), suggesting an 
approaching division, which, however, is never carried out within the series. 
In this section the wood is much thickest on the side opposite the bundles ; 
this is no doubt due to a previous trace, with its attendant roots, having been 
given off in that position at a lower level. The inequality diminishes as we 
proceed upwards, and is finally reversed. 
In the next two sections (Q. 6 and W. 1915 C) there is no change worthy of 
note in the position of the bundles. In the 4th section (Q. 11) one of the 
bundles has been displaced ; the natural interval had increased somewhat, 
and the strands are also appreciably further out. In the 5th section (W. 1915), 
while the strands are still no more than 2*7 mm. apart, they have now 
advanced to a considerable distance beyond the phloem, represented by ten 
or twelve layers of cells. At this level the secondary thiekening is almost 
equal on the two sides of the stele *. 
In the 6th section (W. 1915 B) there is a great change. The same two 
bundles can be recognized, but they have moved much further apart—the 
actual interval is 5 mm., and there does not seem to have been much displace- 
ment. One bundle is cut obliquely, and lies considerably further out than 
the other. The pericycle around the bundles is immensely enlarged (about 
3 mm. thick). Midway between the two strands an adventitious root passes 
out horizontally, and can be traced for some distance. 
In the last section of the series (W. 1915 A) the bundles are still further 
separated (6:5 mm. clear interval). One is still much further out than the 
other, about 1:7 mm. as compared with 0*7 mm. from the stele, but not much 
importance should be attached to this difference, as the section is here 
somewhat oblique and the tissues in places damaged. Only the more remote 
bundle shows signs of division. Both strands are here also imbedded in a 
great mass of apparently pericyclic tissue (see Pl. 2. Phot. 11). A fragment of 
Sparganum hypoderma is present on the outside, but no other cortical 
tissues appear. The whole mass might be taken for a leaf-base, but the 
bundles are not far out enough for this, and one can only regard the excessive 
development on this side of the stem as due to the presence of adventitious 
roots. In this section, as in the last, a root (different from the previous one) 
* It is in this section that the young root, previously figured, occurs ( Williamson & Scott, 
1895, pl. 27. fig. 29). It lies on the side opposite the leaf-trace. 
