ase A SEN 
68 DR. D. H. SCOTT ON THE HETERANGIUMS 
bundles are quite in the outer part of the pericycle, each occupying a very 
marked protrusion of this zone. They are about 1°3 mm. apart, and each 
bundle is tangentially widened and slightły concave on the outer surface— 
indications of approaching division. The bundles are shown in fig. 8 from 
the 4th section (N. 12) where the pericyclic bulges are very prominent, and 
the preparations for division of the bundles evident. Two sections higher up 
the bundles have left the pericycle altogether, and are now in the ill-preserved 
cortex. The further changes consist chiefly in the progress of division in 
each bundle. The trace is shown in fig. 9 from the 9th section (Q. 58), 
where each bundle is distinetly double *. 
This series shows, then, that the trace leaves the stele as a pair of bundles, 
which become widely separated as they pass outwards, and that each of these 
divides into two in the cortex. But the complete division of the two bundles 
into four is not shown. 
This series, however, is of additional interest from the fact that three 
of the sections contain a detached petiole (Pl. 4. fig. 10). The preservation 
is imperfect but the structure is fairly shown. On the outside is a rather 
narrow hypoderma of the * Sparganum" type, with the sclerenchyma exceed- 
ing the parenchymatous bands in extent. The large-celled ground-tissue 
contains two sclerotic patches, in one of which the cells are ranged in rows. 
There are also some scattered elements with contents, which resemble the 
so-called secretory sacs of the stem. 
The petiole measures about 6 x 2:5 mm., and has one side flat, the other 
convex. The important point is that it contains four distinct bundles (shown 
in all the sections). They have been displaced by the intrusion of Stigmarian 
rootlets, but appear to have been in two pairs, those of one pair further apart 
than those of the other. The xylem of the bundles consists of a mass of 
large tracheides, with a band of smaller elements on one side—exactly like 
the strands in the petiole of H. shorense (cf. fig. 3). The organ is obviously 
the petiole of a //eterangium, and there is no reason to doubt that it belongs 
to the stem with which it is associated. Its dimensions relative to the stem 
are about in proportion to those in the Shore plant (H. shorense, stem 
18 mm., petiole 12 x 5'5 mm. ; H. tilieoides, specimen 3, stem, if complete, 
about 10 mm., petiole 6 x 2:5 mm.). 
This specimen, then, establishes the strongest presumption that the petiole 
of FI. tiliwoides contained four distinct vascular bundles, confirming the 
evidence for a quadruple leaf-trace derived from the stem. 
To complete the proof it is clearly desirable to observe the structure 
of a leaf-base still in connection with the stem. This is shown, though 
* One of the double bundles is figured by Williamson (1887, pl. 22. fig. 7) from W. 1623, 
the 7th section. 
