92 



" When not highly magnified, and where the structure is not well 

 preserved, some of the larger ducts appear as if they had a spiral 

 fibre wound round them, as shown in fig. 3 ; but when more highly 

 magnified in a part where the structure is well preserved," it is 

 found to result from such markings as are shown by the larger duct 

 in fig. 4. The very elongated ovals shown in the lower part of it are 

 on the outside of the membrane of which the duct is composed, and 

 the circular ones are on the inside. This is readily shown by the 

 focal adjustment, and by the manner in which they occur when the 

 duct is cut through in making the section, as is common in recent 

 exogenous wood, the ducts often contain irregular membranous divi- 

 sions, as will be seen from all the drawings. 



There can thus be no question of this wood being a true non-gym- 

 nospermous exogen; and its occurrence in the lias is of course 

 a fact of considerable interest, as proving that trees of that character 

 existed at a much earlier period than has hitherto been generally 

 supposed. 



I have made many sections of woods belonging to various natural 

 orders of exogens, with a view to learn whether the natural affinity 

 of the fossil could be determined from its structure, but have been 

 unable to determine any rules from which this could be ascertained ; 

 though a much more extended examination might perhaps solve the 

 question. 



