XXIX] 



LYGINOPTERIDEAE 



39 



i. Stem. 



The petrified stem on which Binney founded the species was 

 first figured by Dr Arber^ from a section in the Binney collection 

 in the Sedgwick Museum, Cambridge: this section (13mm. in 

 diameter) is reproduced in fig. 402. The most striking features 

 are: (i) the pith consisting of an unusually large and irregular 

 group of dark thick-walled parenchyma, (ii) the broad cylinder 

 of manoxylic secondary xylem characterised by multiseriate 

 medullary rays, (iii) the outer cortex composed of dark radially 



Fia. 402. Lyginopteria oldhamia. Transverse section of the type-specimen in 

 the Binney Collection, Sedgwick Museum, Cambridge. (After Arber.) 



disposed and oblique bands of mechanical tissue separated from 

 one another by partially destroyed and tangentially elongated 

 parenchymatous elements. It is this outer cortex that Williamson 

 aptly compared with the Eoman numerals on a clock-face. In 

 the perimeduUary region and in contact with the inner edge of 

 the secondary-xylem cylinder are six strands of primary xylem 

 1 Arber, E. A. N. (02). 



