CUPRESSOXYLON 243 



.05 mm. in short, diameter. In the summer wood the cells become 

 smaller and more nearly hexagonal in outline, and pass abruptly into 

 the band of fall wood. 



''Radial. In this section, as in the transverse, the demarcation between 

 fall and spring wood is very clearly marked. The walls of the cells 

 in the spring and summer wood are the only ones provided with bor- 

 dered pits, and in these they seem not to have been very abundant, 

 or at least are not preserved in a manner capable of demonstration. 

 These pits are usually arranged in 2 parallel rows, although in some 

 cases there is but i row, when it occupies the center of the cell. The 

 pits are large, and when in 2 rows take up nearly the entire width 

 of the cell. The diameter of the outer circle is in extreme cases 

 fully .025 mm., the average being about .02 mm. ; the diameter of the 

 inner circle is only .oo25-.oc>4 mm. The medullary rays are observed 

 to be numerous, with the individual cells very long. The latter are 

 not, however, very high, and they are thin-walled. The pits on the 

 lateral walls are not recognizable. The resin ducts are moderately 

 numerous. They are composed of a chain of short, thin-walled cells 

 .15-. 25 mm. in length, and are partially filled with a dark mass repre- 

 senting the resin. 



" Tangential. In this section the medullary rays are observed to be com- 

 posed of a single series of cells which ranges from 3 to 30 in number. 

 It is rare, however, to find them with as few as 3 or as many as 30 

 cells, the average number being from 8 to 15. Bordered pits have 

 not been observed in this section" (Knowlton). 



Material silicified. 



Cretaceous (?) of Emmet County, Iowa (Knowlton). 



20. C. McGeei, Knowlton 



" Transverse. The tracheids are arranged in strictly radial rows. The 

 annual ring is broad, consisting in some cases of as many as 50 or 

 60 of the larger, and 10-16 of the smaller, thick-walled cells. The 

 larger cells are mostly quadrangular in outline and have a diameter in 

 some instances of .08 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 ad- 

 ditional rows of tracheids have been intercalated. The medullary rays 

 are moderately numerous. 



" Radial. The large size of the tracheids is very clearly shown, and they 

 make up the bulk of the section. The tracheids of 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 2, and in some exceptionally large cells, in 3 rows. 

 They are also very large, the outer circle having a diameter of .02 

 .025 mm., and the inner of .005 .008 mm. The walls of the medul- 

 lary rays are marked by large, oval pores, from I to 3 of which 

 occupy the width of a single wood cell. The resin ducts consist of 

 a chain of short, small, thin-walled cells, which now contain a small 

 quantity of granular matter, representing probably drops of resin. 



