ON LEPIDOPHLOIOS SCOTTII. 445 



General Structure. 



The plant of which the fragments formed parts must have been fairly tall, for, in 

 these stems, there is no change in the various tissues throughout their length. There 

 are slight differences between the individual pieces, chiefly as regards the amount of 

 periderm developed. 



No single section shows all the tissues in organic continuity, while some tissues, 

 notably the phloem, are hardly to be distinguished in any section. Taken conjointly, 

 figs. 1 and 8 give a fairly good idea of the transverse appearance, all the parts, from 

 central xylem to the leaf- bases, being organically connected. The xylem at first sight 

 appears solid, but careful examination reveals the presence of short, thin -walled cells 

 distributed near the centre of the xylem, either in groups or occupying the whole of the 

 centre (see p, figs. 2, 2a, and 4 respectively). Scattered through this parenchyma as 

 detached strings of cells, or more often between the short-celled parenchyma and the long 

 tracheides of the primary wood, are short, reticulately thickened tracheides with flat ends. 

 In fig. 2, t', the ends are shown, and in fig. 5, if, these cells are cut longitudinally. 

 These tracheides vary greatly in length, being sometimes broader than long, and 

 occasionally they attain a length of from three to four times their width. In Lepidophloios 

 Scottii the pith shows a transitionary condition between those lycopods with solid xylem 

 and those with a true medulla. The scattered tracheides in the pith have departed less 

 in their character from those of the primary wood than is the case in Lepidodendron 

 vasculare (Binney, sp.). 



The primary wood is composed of scalariformly thickened, centripetally developed 

 tracheides (fig. 5, t). No secondary wood has been observed in any of the specimens, 

 but other secondary tissue has been developed in successive zones, so that the stems 

 are not of only one season's growth. The protoxylem is peripheral, occurring as blunt 

 points round the woody axis. The leaf-traces have a mesarch xylem and rise abruptly 

 at first, but, after crossing the middle cortex, they bend out horizontally into the leaf- 

 bases (fig. 4, l.t). 



Owing to imperfect preservation, the phloem is distinguished with some difficulty, but 

 a zone of partially disintegrated tissue surrounding the xylem probably represents it 

 (fig. 1, ph.). Outside the phloem zone is a layer of cells tangentially elongated, probably 

 marking the outside limit of the inner cortex. The middle cortex is well preserved only 

 in Dr Scott's specimen (fig. 1, m.c), and in one of my stems near the end, and consists 

 of thin-walled parenchyma. There is no trace of secondary tissue in this zone. The 

 outer cortex is separated from this middle belt by a layer of tangentially elongated cells, 

 two or three rows deep, with thin walls, which passes gradually into the thicker-walled 

 outer cortex. The outer cortex consists of three zones, the inner being parenchymatous, 

 the middle prosenchymatous, and the outer parenchymatous. The elements of these 

 zones are more or less radially arranged, but the outer zone passes into a more irregular 

 parenchyma on which the leaf-bases abut. 



