96 DR. D. H. SCOTT ON THE HETERANGIUMS 
H. Schusteri (Kubart, 1908, fig. 3; 1911, p. 11; 1914, p. 3) is inter- 
mediate, as regards the stelar structure, between H. Sturt? and H. alatum ; 
the peripheral xylem-strands are only slightly differentiated. Nothing is said 
about the position of the protoxylem ; from the figure it appears to lie rather 
far out, approaching //. Sturi? in this respect. The figure shows three leaf- 
traces very clearly, one just starting as a single strand, another, in the 
pericycle, somewhat constricted, and a third, also in the pericycle, just divided 
into two. The plant thus falls under /u-heterangium, resembling our 
H. minimum in the division of the originally single trace. 
LI. Andrei (Kubart, 1914, p. 4, Taf. 2. fig. 4) is the most interesting of 
the five species, as it shows a transition towards Lyginopteris. The 
transverse section of the large stem shows quite the anatomical habit of a 
Lyginopteris ; the primary tracheides, however, extend to the centre of the 
pith, where they are scattered and intermixed with much parenchyma. The 
peripheral strands of the xylem are quite distinct and few in number, as in 
Lyginopteris; the leaf-trace starts from the stele as a single bundle, which 
divides into two, much as in Lyginopteris oldhamia. In sections lent me 
by Dr. Kubart, which I have no doubt were of the species subsequently 
named by him H. Andrei, I found in connection with the stem a leaf-base 
containing four bundles, as well as detached petioles with the same 
structure *. It appears, then, that Æ. Andrei unites the characters of our two 
subgenera, a single trace leaving the stele and ultimately dividing into four 
in the leaf-base. This fact, if confirmed, would be a fatal objection to the 
establishment of a new genus for the polydesmic forms, but our provisional 
subgenera may still serve a useful purpose. Possibly Dr. Kubart may 
eventually suggest a third subgenus for the Lyginopteroid species of 
Heterangium. We are not here concerned with Dr. Kubart’s new species of 
Lyginopteris, but may mention that L. heterangioides (Kubart, 1914, p. 4, 
Taf. 2. fig. 5) is a typical member of that genus, except for the constant 
presence of a few tracheides about the middle of the pith, an evident vestige 
of the metaxylem of Heterangium, already becoming reduced in M. Andrei. 
A species from the coal-field of the Ruhr (Westphalia), named //. inter- 
medium by Kubart (1914, p. 6), is described as forming a link between 
Heterangium Andrei and Lyginopteris heterangioides : we have, in fact, as 
the discoverer points out, a continuous series leading gradually from the 
protostele typical of /7eterangium to the siphonostele typical of Lyginopteris. 
To return to our more immediate subject: the result of our survey is to 
show that the older species of /Jeterangium tend, on the whole, to belong to 
the simpler Hu-heterangium type, while the later species for the most part 
show the more complex structure which characterizes the proposed subgenus 
Polyangium. 
* I noticed long, stalked glands on both stem and petiole—a very Lyginopteris-like 
feature, 
