418 Systematic Paleontology 



by the pressure to which it had been subjected. The bark was not 

 preserved in any of the pieces examined. 



"Microscopic analysis. — Transverse section: This section shows the 

 tracheids to be arranged in strict radial rows, and also indicates their 

 great size. The annual ring, as above stated, is broad, consisting in some 

 cases of as many as fifty or sixty of the larger and from ten to sixteen 

 of the smaller, thick-walled cells. The larger cells are mostly quad- 

 rangular in outline and have a diameter in some instances of .080 mm., 

 the average being about .068 mm. The cells of the fall wood have very 

 thick walls and are much flattened. Intercellular spaces are frequently 

 observed, particularly where additional rows of tracheids have been 

 intercalated (pi. Ixix, fig. 1). The medullary rays are moderately 

 numerous. 



^ " Radial section. — The large size of the tracheids is very clearly shown 

 in this section, most of which is made up of summer wood. The 

 tracheids in the fall wood are, of course, much smaller and are covered 

 with but a single row of pits. The bordered pits are very close together 

 on the summer wood and are always in two and in some exceptionally 

 large cells in three rows. They are also very large, the outer circle 

 having a diameter of from .020 mm. to .025 mm., and the inner of from 

 .005 mm. to .008 mm. The walls of the medullary rays are marked 

 by large oval pores, from one to three of which occupy the width of a 

 single wood cell. These pores are about .015 mm. in length and .010 

 mm. in the short diameter. The resin ducts consist of a chain of short, 

 small, thin-walled cells, which now contain a small quantity of granular 

 matter, representing probably the drops of resin. The individual cells 

 have a length of from .12 mm. to .25 mm., and a diameter of about .05 

 mm., slightly less, it will be observed, than the tracheids among which 

 they run. 



" Tangential section. — ^The medullary rays are always simple ; that is, 

 they consist of but a single row of cells, which varies from 2 to 49 cells 

 in height. The tracheids are provided on the tangential walls with a 

 few scattered bordered pits. These have a diameter of from .016 mm. 

 to .021 mm."— Knowlton, 1889. 



