ARAUCARIOXYLON 207 



are then nearly circular in outline and have a diameter of o.oi 7-0.02 mm. 

 When there are 2 rows they are in contact and alternate with each 

 other, and have a nearly regular, hexagonal outline. These hexagonal 

 pits have a diameter of o.oi6-.o2i mm. The inner pore is very small, 

 being only about .002 5-. 003 mm. in diameter. 



" Tangential. The rays are single and range from 1-27 cells in height, the 

 average number being about 10-12" (Knowlton). 



Material silicified. Specimen represented by a small fragment. 

 From the Potomac Formation at Taylorsville, Virginia (Knowlton). 



6. * * A. Prosseri, Penh. 



Transverse. Tracheids in regular radial rows, squarish, 39 x 42 p broad ; 

 the walls 6.2 p. thick. Resin cells and special resin passages wholly 

 wanting. No evidence of growth rings in a radial extent of 22 mm. 



Radial. Ray cells all of one kind, straight or narrower at the ends, equal to 

 3-9 tracheids ; the upper and lower walls thin and devoid of pits ; the 

 terminal walls thin, not pitted, curved ; the lateral walls show no struc- 

 ture through extreme alteration. Bordered pits not clearly determinable, 

 but probably round and in i row. 



Tangential. Rays numerous, chiefly low ; the cells broad, round, about 31 ^ 

 wide. 



Material silicified. 



The Cheyenne (Comanche Cretaceous) of the bluff west of Sun City, Medi- 

 cine Lodge River, Baker County, Kansas, 1897 (Prosser). 



7. * * A. arizonicum, Kn. 



" Transverse. Annual rings not apparent to the naked eye, but under the 

 microscope observed to be present, the yearly growths being separated 

 by a layer of 2-5 tangentially compressed cells ; the tracheids in this 

 section are observed to have moderately thick cell walls, and to be 

 separated by small intercellular spaces. The largest cells observed have 

 a diameter of .055 mm. and the smallest of about .020 mm., the average 

 being about .040 mm. 



" Radial. As seen in this section the tracheids are observed to be long, and 

 to be provided with numerous pores. These pores or bordered pits 

 are usually arranged in a single series, and number 40-80 or more on 

 each cell. Usually they touch each other slightly, but sometimes they 

 become a trifle compressed by actual contact. When these pores are 

 arranged in 2 series they alternate and are slightly, if at all, angled by 

 mutual pressure. The pores are rather large, the average diameter for 

 the outer circle being about .02 mm., that for the inner .0040 mm. The 

 medullary rays are composed of short, thin-walled cells, which, in some 

 instances, seem to have been provided with small, oval pores. They are 

 difficult of demonstration, and it is possible that the granular contents 

 of the cells may give the appearance of exterior markings. 



" Tangential. This section demonstrates the presence of pores or bordered 

 p'its on the tangential walls, a circumstance of infrequent occurrence 



