164 LYCOPODIALES [<^H. 



visited the locality and published an account of the peculiar 

 method of preservation of the plant remains ^ It is, however, to 

 Williamson^ that we owe the more complete description of these 

 Arran stems. Portions of large stems from the Arran beds are 

 preserved in the British Museum, the Sedgwick Museum, Cam- 

 bridge, and in the Manchester Museum. The section of one 

 of these is shown in fig. 180; an outer shell of bark encloses a 

 mass of volcanic ash in which are embedded several woody 

 cylinders originally described as "internal piths^" and by Carru- 

 thers as young stems produced from spores which had germinated 

 in the hollow trunk of a large tree. The true interpretation was 

 supplied by Williamson who showed that a stem of the dimensions 

 of that represented by the outer cortex, e, fig. 180, must have 

 possessed a single stele of the size of those seen in the interior 

 of the hollow trunk. The additional woody cylinders, or steles, 

 were derived from other stems, and carried, probably by water, 

 into the partially decaj'ed trunk. In addition to large Lepido- 

 dendron stems Williamson described smaller shoots as well 

 as an Halonial branch and made brief reference to some 

 cones described by Binney^ in 1871 from the same locality. 



The following account of Lepidodendron Wiinschianum is 

 based on an exceptionally fine specimen discovered by Mr T. 

 Kerr of Edinburgh in Calciferous sandstone volcanic ashes at 

 Dalmeny in Linlithgowshire. The material from this locality 

 described by Mr Hill and myself" was generously placed in my 

 hands by Dr Kidston of Stirling. Fig. 181, A, shows a 

 transverse section, 33 cm. in diameter, consisting of a shell of 

 outer cortical tissue enclosing a core of light-coloured volcanic 

 ash; on the decay of the more delicate middle cortex the cylin- 

 drical stele dropped to one side of the hollow trunk. The stele, 

 fig. 182, has a diameter of 6-5 cm.; the centre is occupied by 

 concentric layers of silica, s, surrounded externally by the 

 remains of a parenchymatous pith, p, made up of isodiametric 

 and sinuous hypha-like elements like those in the middle cortex 

 of Lepidodendron shoots. On the inner edge of the primary 



1 Carruthers (69). a Williamson (80) A. ; (93) ; (95). 



3 Wiinsch loc. cit. * Binney (71) p. 56. 



5 Seward and Hill (00). 



