772 GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. 



form high plates of cells, the exact length of which can not be determined 

 with satisfaction. If there were markings on the rays they can not be seen; 

 neither can the markings on the dncts be observed. 



Tangential section. — This section shows much better under the microscope 

 than the radial one. 



The rays are found to be of two distinct kinds: The most numerous 

 are only 1 cell broad and from 10 to 25 cells high, the individual cells 

 being thin-walled and oblong in shape. At scattered intervals are very 

 broad rays composed of 10 to 20 rows of cells and extending for long- 

 distances through the section (see fig. 2 of PL CXXI). These broad rays 

 are often somewhat cut by wood cells passing diagonally through them 

 (see fig. 2 of PI. CXXI). This does not, however, interfere with the ray 

 as a whole, which is clearly demarked from the small ravs of a single 

 series of superimposed cells. The individual cells of the large rays are 

 nearly circular in cross section, or more or less 6-sided by mutual pressure. 

 They are also thin-walled. 



Associated with the small rays is usually a layer or two of short-celled 

 tissue or series of parenchymatous cells. Except for there being shorter 

 cells the}^ are not to be distinguished from the ordinary wood cells. 



The ducts show clearly enough in this section, but they are not well 

 enough preserved to permit the markings on the walls to be made out. It 

 would seem that the walls were pitted, but this is largely surmised. 



A considerable number of species of Quercinium, 1 or oak wood, in a 

 fossil state, have been described from various parts of the world. Wood 

 of this kind is readily distinguished by the large isolated ducts and the two 

 kinds of medullary rays. 



The species under consideration resembles a number of described 

 forms, but they are all from the Old World, and are readily distinguished 

 from it. 



This species is closely allied to Quercinium knowltoni Felix, and may 

 possibly be the same, but as Felix's species is not fully illustrated it is 

 difficult to be positive. Q. lamarense seems to differ in the shape and size 

 of the large ducts, but it will need a careful comparison of the sections to 

 be positive. For the present, at least, they may remain distinct. 



Habitat: Specimen Ridge, Yellowstone National Park; specimen from 



1 Fifteen species and varieties. 



