V] TRACES OF WOOD-BORERS IN PETRIFIED TISSUE. 107 



appearance is due to the deposition of mineral matter on the 

 inside of the thin cell-membrane. Examples of such sources 

 of error as have been briefly referred to, and others, will be 

 found in various parts of the descriptive portions of this book. 



There is one other form of pitfall which should be briefly 

 noticed. In sections of petrified plants one occasionally finds 

 clean cut canals penetrating a mass of tissue, and differing in 



Fig. 24. A. Section of partially disorganised tissue attacked by some boring 

 animal, c, c, coprolites ; d, a tunnel made by the borer through the plant 

 tissue. 



B. Transverse section of a Lepidodendroid leaf, of which the inner 

 tissues have been destroyed and the cavity filled -with coprolites ; simulating 

 a sporangium containing spores. (A and B from specimens in the Botanical 

 Laboratory collection, Cambridge.) 



their manner of occurrence and in their somewhat larger size 

 from ordinary secretory ducts. Such tunnels or canals are 

 probably the work of a wood-boring animal. An example is 

 illustrated in fig. 24 A. Similarly it is not unusual to meet with 

 groups or nests of spherical or elliptical bodies lying among 

 plant tissues, and having the appearance of spores. Such 



