528 STUDIES IN FOSSIL BOTANY 



of growth, but, generally speaking, annual rings cannot 

 be distinguished. 



The medullary rays are narrow ; the principal rays, 



P p* ep sc k 



Fig, 190. — Coi-daites (Araucarioxyloii) Brandlingii. A, Radi.il section (somewhat 

 restored) of middle part of stem, showing discoid pith (/) and wood (_r). x about 7. 

 R, Inner part of wood, with adjacent cells of pith, in radial section. /, pith-cells ; 

 px, narrow spiral tracheides of protoxylem'; sp, wider spiral tracheides ; sc, scalari- 

 form tracheides ; bt, tracheides with bordered pits, x 95. Kidston Coll. 185 (Coal- 

 measures of Dudley). (G. T. G.) 



between the original bundles, may be as much as three 

 cells in thickness, but the secondary rays are usually 

 one, or at most two cells thick. The narrow rays have 



