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DR. D. H. SCOTT ON THE HETERANGIUMS 
HETERANGIUM TILLEOIDES, Will. 
The anatomy of the stem of this well-known species from the Halifax Hard 
Bed has been fully described (Williamson, 1887; Williamson & Scott, 1895) 
and need not be recapitulated here. The species is remarkable for the great 
development of the phloem, sometimes equalling that of the secondary wood, 
and for the characteristic form of the main phloem-rays, dilated outwards 
like those of the Lime Tree. The specimens are among the most beautifully 
preserved of petrified plants, so far at least as the stelar tissues are 
concerned. 
Only three points demand our attention—the course of the leaf-traces, the 
adventitious roots, and the specific distinction from other members of the 
genus. 
The Leaf-traces. 
No satisfactory account of the course of the leaf-traces has ever been given. 
Williamson, in his original description of the species, mentions and figures 
“ascending vascular bundles grouped in pairs” (Williamson, 1887, p. 290), 
and further speaks of “the twin bundles going off to what, both in this plant 
and the allied Aeterangium Grievii, I presume to have been petiolate leaves iil 
(L. e. p. 293). 
In our joint memoir (Williamson & Scott, 1895, p. 763) it was recognised 
that the twin bundles with secondary wood just leaving the stele, already 
figured by Williamson in 1887, represent a double leaf-trace. Thus the 
trace was shown to start as a pair of distinct bundles. On the other hand, 
the conjecture that “ the twin bundles may have completely fused on entering 
the leat” has proved to be incorrect. The reverse is the case. 
Beyond the fact that the leaf-traces were double, nothing definite was, in 
fact, established as to this part of the anatomy of Æ. tiliwoides. 
Thanks to the kind help of Prof. F. W. Oliver and Prof. F. E. Weiss in 
lending slides from their collections, I have been able to examine most, if 
not all, of the sections of this species in this country. Good as the sections 
are for anatomical details, the material is not particularly favourable for 
following the course of theleaf-traces. This is owing partly to the absence 
of continuous series of sufficient length and partly to the fact that in this 
species the cortex is usually the worst-preserved region of the stem, so that 
the leaí-traces are imperfectly shown in the outer part of their course. Still, 
it has been possible to determine the essential points. 
The sections of Æ. tilimoides which have come under observation appear to 
belong to four distinet stems, reckoning only those which clearly belong 
to this species. Three of these are represented in the Williamson Collection, 
and sections from them are described and figured in his original memoir of 
1887. These may be regarded as types. The fourth specimen is represented 
in my own collection and that of the Manchester Museum. A synopsis of 
