xv] 



LEPIDODENDRON 



121 



An example of a large and partially decorticated stem is 

 afforded by the specimen (16 x 7*5 cm.) shown in fig. 153. The 

 irregularly ribbed surface is formed of rather thick-walled 

 phelloderm, in which occur tangentially arranged rows . of 

 secretory strands. The tapered form of the secondary cortex 

 as it abuts internally on the primary cortex is shown very clearly 

 in the drawing (cf fig. 151, C). The stele in this much older 

 stem consists mainly of secondary wood. 



Pig. 154. Lepidodendroti vasculare. Shoot (2-8 cm. diam.) with two steles. 

 (From a specimen from Halifax in the Williamson Collection, 

 British Museum, No. 340.) 



An interesting example of a small shoot, the largest 

 diameter of which is 2'8 cm., is shown in fig. 154, A : the section 

 was cut a short distance above the bifurcation of the stele into 

 two approximately equal branches. The outer part of the 

 cortex consists of phelloderm, pd, with the usual rows of 

 secretory tracts, and primary outer cortex g ; the middle cortex 

 is represented by patches of parenchyma with a few leaf-traces. 

 To one of the steles, s' (fig. 154, A), a crescent-shaped band of 



