170 LYCOPODIALES [CH- 



employed by Scott and Weiss. Between the secretory zone and 

 the outer cortical region, no tissues have been preserved. The 

 shell of bark consists chiefly of radial rows of elongated cells 

 with rather thick walls characterised by the occurrence of small 

 intercellular spaces and by tangentially placed bands of secretory 

 cells and sacs (fig. 181, D, s). Immediately internal to the 

 secondary cortex or phelloderm occur groups of secretory tissue 

 as shown in the section of L. Harcowtii (fig. 179, B). 



The large tree shown in transverse section in fig. 181, A, 

 has lost its leaf-cushions; the bark, as seen in the lower 

 part of the photograph, presents a fissured appearance like 

 that with which we are familiar on an old Oak or Elm stem. 

 A radial longitudinal section through the phelloderm revealed 

 the existence of a crushed leaf-trace passing outwards in an 

 approximately horizontal course accompanied by a strand of 

 parenchymatous tissue^ having the characteristic structure of a 

 parichnos. It is probable that the surface of this partially 

 decorticated stem differed in appearance from that of an old 

 Sigillaria (cf. fig. 198) in the much smaller and less conspicuous 

 parichnos strands. 



In addition to the large stems of L. Wunschianum from 

 Arran and Dalmeny numerous examples of smaller axes from 

 the former locality are represented in the Williamson collection 

 (British Museum). Some of the twigs are characterised by a 

 solid stele (protostele) giving off numerous leaf-traces, accom- 

 panied by short spirally thickened tracheids like those which 

 occur at the outer edge of the primary xylem in the larger stem: 

 these extend into the leaf where they are arranged round the 

 vascular bundle like the transfusion tracheids^ in many recent 

 conifers. The surface of these smaller shoots bears large leaf- 

 cushions which are seen in longitudinal section to have the form 

 characteristic of Lepidophloios. It is worthy of note that a 

 section of a bifurcating axis of this species from the Calciferous 

 Sandstone of Craigleith (British Museum Collection'), although its 

 diameter is 19 x 14 cm., shows no signs of secondary wood. This 

 late appearance of secondary xylem and other anatomical features 



1 Seward and Hill (00) PI. ii. fig. 14. a Worsdell (95) ; Bernard (04). 



•* No. 52, 625. 



