XVI] 



SIGILLARIA 



205 



in France, the parichnos scars reach a length of 3 cm. As seen 

 in the fragment of a ribbed Sigillaria represented in fig. 198, 

 the large parichnos areas exhibit a distinct surface pitting in 

 contrast to tlje fine longitudinal striation of the rib ; the 

 difference in surface-appearance is due to the nature of the 

 tissue, which in the parichnos consists of fairly large parenchy- 

 matous elements with groups of secretory cells ^ and in the 

 exposed cortex of elongated elements. The vertical line in the 

 middle of fig. 198, which occurs in the middle of the rib, has 

 probably been formed by splitting of the bark. 



Fig. 198. SiSfiZ^arm with large parichnos areas. (^ nat. size.) M.S. 



Grand'Eury's description of fossil forests of Sigillariae in 

 the rocks of the St :6tienne= district affords a striking picture of 

 these arborescent Pteridophytes ; he speaks of the stems of some 

 of the trees as swollen like a bottle at the base, characterised 

 by the Syringodendron features and terminating below in 

 short repeatedly forked roots of the type known as Stigmari- 

 opsis. Other specimens of Sigillaria stumps show a marked 

 decrease in girth towards the base; this tapered form is 

 regarded by Grand'Eury as the result of the development of 

 aerial columnar stems from underground rhizomes. 



The nature of the root-like organs of Sigillaria is dealt 

 with in the sequel : a brief reference may, however, be made 



1 Coward (07) ; Renault (9C) A. 



2 Grand'Eury (90) A. PI. in. 



