IV] 



FOSSIL PLANTS IN VOLCANIC ASH. 



89 



petrified plants of Carboniferous age occur in such preservation 

 as allows of a minute investigation of their internal structure. 

 The occurrence of plants in the former locality was first discovered 

 by Mr Wiinsch of Glasgow ; the fossils occur in association with 

 hardened shales and beds of ash, and are often exceedingly well 

 preserved \ In fig. 18 is reproduced a sketch of a hollow tree 

 trunk from Arran, probably a Lepidodendron stem, in which 

 only the outer portion of the bark has been preserved, while 

 the inner cortical tissues have been removed and the space 

 occupied by volcanic detritus. 



The smaller cylindrical structures in the interior of the 

 hollow trunk are the central woody cylinders of Lepidodendroid 

 trees; each consists of an axial pith surrounded by a band 



Fig. 18. Diagrammatic sketch of a slab cut from a fossil stem {Lepidodendron ?) 

 from Laggan Bay. e, Imperfectly preserved bark of a large stem, extending 

 in patches round the periphery of the specimen ; the oval and circular bodies 

 in the interior are the xylem portions of the central cylinders of Lepidoden- 

 dron stems, x^, primary wood, x^, secondary wood. From a specimen in the 

 Binney collection, Woodwardian Museum, Cambridge. \ nat. size. 



of primary wood and a broader zone of secondary wood. One 

 of the axes probably belonged to the stem of which only the 

 shell has been preserved, the others must have come from other 



1 Bryce (72) p. 126, fig. 28. 



