Johnson — A Seed-Bearing Heterangium from Co. Cork. 249 



almost certainly was like Lyginodendron oldhamium (Crossotheca Rcenincjhaim 

 Kidston sp.), a Pteridosperm of the group Lyginodendrese. Its angular 

 stem, rarely branched, formed adventitious roots, and bore large compound 

 pinnate, fern-like leaves, spirally arranged with a divergence of f or f. 

 Its stem shows a central Grleichenia-like monostelic or haplostelic vascular 

 axis, without pith. Its peripheral or peri- medullary mesarch primary xylem 

 is arranged in indistinct groups with internal metaxylem mixed with con- 

 junctive parenchyma, occupying the position of the pith. Secondary thickening 

 of regular character (xylem within, phloem without) occurred, though no stem 

 is known more than 2 cm. wide, the average diameter being TS cm. (The 

 Bear Island specimen doubtfully referred to Heterangium by Nathorst has a 

 diameter of 3 em.) The tracheids, other than the protoxylem ones, show 

 multiseriate bordered pits on their radial walls. Very striking to the naked 

 eye is the transverse striation, which was shown by Williamson to be caused 

 by horizontal plates of rounded sclerotic cells arranged in vertical rows in the 

 inner cortex. The surface of the stem is also longitudinally striate, owing to 

 peripheral sclerotic strands comparable with those forming the network in 

 Lyginodendron, but running almost vertically. The phyllotaxis, elaborately 

 worked out by Stur, was independently ascertained by Williamson by the 

 study of the internal anatomy. The transverse striation is continued into 

 the rachis, which presents on its upper side a deep median groove with a 

 ridge on either side. The under side of the rachis is convex. The striae are 

 best seen as a single row in the adaxial groove, but are not confined to it- 

 Judging from the pronounced transverse striation of Sphenopteridium rigidiim 

 (Ludw.) Pot., and S.furcillatum (Ludw.) Pot., as described and figured by 

 Potonie (8) in the rachis of these two fossil plants from the Upper Silurian (?) 

 beds of the Harz Mountains, they will be found when more complete specimens 

 are available to be members of the Pteridosperms. It is worthy of note in 

 passing that Potonie compares the two species with S. elegans, now recognized 

 as the foliage of Heterangium Grievii. Again, the Rhodea dissecla (Brgt.) 

 Presl, figured by Potonie (9) as synonymous with Diplothmema Schilizei 8tui, 

 differs only in its smaller size from D. elegans i.e. Heterangium Grievii, and is 

 clearly a Pteridosperm — a view already held by Kidston (10). The single 

 leaf-trace bundle arises opposite the primary xylem, and is in direct con- 

 tinuity with it. It at once passes out from the pericyele into the cortex to 

 run through 7-8 internodes, 2 cm. high, before entering the base of the 

 rachis as a solitary trace. The bundle is at first collateral and exarch, but 

 becomes concentric in the rachis. SufEeient has been said to show that, from 

 a study of the vegetative organs alone, the evidence was strong enough to 

 justify the inclusion of Heterangium in the new transitional group of 



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