PALEOZOIC CONE-GENUS LEPIDOSTEOBUS. 213 



pliotograplied in PL 21. fig. 4, but their position can be made out. They are visible in 

 longitudinal section in PL 22. fig. 5. The number of tracheides on any radius between 

 the pith and the protoxylem (px.) is about four. The contrast in size between the 

 scalariform metaxylem [mx.) and the spiral protoxylem elements is unusually great 

 (PL 21. fig. 4 and PL 24. figs. 18 & 19). The horizontal bars of thickening on the walls 

 of the metaxylem tracheides are connected by delicate vertical striations (PL 24. fig. 18). 

 There seems to be a complete or almost complete absence of the short barred tracheides 

 characteristic of the peripheral zone of the xylem in L. oldUamius, Will, (a) *. The 

 phloem is not preserved. The firm inner cortex (i.e., PL 21. fig. 4) is four to five 

 elements in thickness. As is usually the case in Lcpidostrohus, the middle cortex has 

 perished, but the outer cortex survives. 



A 



(4) The Sporophyll Traces in the Axis. 



We only possess a single radial longitudinal section of L. Bimerjams f, and this is 

 somewhat imperfect. Tlie sporophyll traces, as shown in this section, were peculiar in 

 following an obliquely downward path in the outer part of their course from central 



cylinder to sporophyU [l.t., PL 24. fig. 21). 



* PL 24. fig. 22 shows a sporophyll trace, as it appears in transverse section while 

 traversing the space immediately outside the central cylinder. The xylem, which is 

 alone preserved, consists of a compact group of seventeen tracheides ; there are two or 

 three small elements occupying a central position which possibly may be the protoxylem. 

 As the sporophyll traces pass through the inner cortex, they each become invested with a 

 sclerised sheath, which accompanies them on their outward journey (Lc.s., PL 21. fig. 4 

 and PL 24. fig. 23). As a rule, the xylem alone is preserved, but occasionally a small 

 detached group of elements is also visible on the outer side of the xylem ; this may 

 perhaps represent the phloem. The xylem group, which is roughly circular while the 

 trace is still close to the vascular cylinder (PL 24. fig. 22), becomes narrowed radially 

 and widened tangentially as it passes further out (PL 24. fig. 23). The sporophyll traces 

 in the middle cortical sheath are too much distorted for measurement, but before they 

 become free from the inner cortex their tangential width (including the sheath) is about 



0*15 mm. 



(5) The Detailed Structure of the Sporophyll 



The dimensions and general form of the sporophyll have already been briefly mentioned. 

 A noticeable feature of the winged sporophyll pedicel, when viewed in tangential section, 

 is the occurrence of a cushion of sclerised elements on either side of the median attachment 

 of the sporangium. Many of the cells of the cushion are so thick- walled that their 

 cavities are almost or entirely obUterated {sec.. H. 22. figs. 7 & 8 and PL 25. figs. 26, 26 «, 

 & 27). On the lower side of the pedicel there is a well-marked keel, of which the histology 

 is somewhat unusual. The epidermal layer {ep.) of small cells is succeeded internally by a 

 hvpoderma (liy.) of large cells with firm walls. These are markedly distinct from the 



Maslen, A. J. ('99), p. 362. t Q- «• 6. 



SECOND SEr.IES. — BOTANY, VOL. VITT. 



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