SEQUOIA 227 



Radial. Bordered pits large, in 1-2 rows. Medullary rays often with a 

 large resin passage bearing thyloses ; the cells all of one kind ; the 

 upper and lower walls thin and much altered by decay ; the lateral 

 walls devoid of recognizable markings. 



Tangential. Ordinary rays i- or sometimes 2-seriate in part ; the fusiform 

 rays with large resin passages containing thyloses. 



An exceedingly well-characterized species from the Eocene of the Porcu- 

 pine Creek and Great Valley groups. 



5. * * S. magnifica, Knowlton 



"Trunks often of great size, 6-10 feet in diameter, 30 feet high as now 

 preserved, bark when present 5 or 6 inches in thickness ; annual rings 

 very distinct, 2-3 mm. broad." 



" Transverse. In this section the structure appears beautifully preserved. 

 The rings are rather narrow, being only 2 or 3 mm. broad, or often 

 only i mm. They are very sharply demarked, even to the naked eye. 

 Under the microscope the rings are found to consist of a band of 

 thick-walled cells that is never more than 15 rows of cells deep and 

 often reduced to 2 or 3 rows. The cells composing the spring and 

 summer wood are of uniform size and inclined to hexagonal in shape. 

 Those of the fall wood are, of course, compressed. 



" The resin cells are numerous and may be readily distinguished 

 by the dark contents. They occur mainly in the spring and summer 

 wood. 



" The medullary rays seen in this section are long, straight, and 

 separated by usually about 3 rows of wood cells." 



"Radial. This section is the least satisfactory of all. The wood cells 

 show well under the microscope, but their markings are very obscure. 

 By prolonged search it is made out that the pits are in i row, or some- 

 times 2 parallel rows. They are small, as far as can be made out, 

 and are too obscure for satisfactory measurement. 



" The rays are composed of long, unmarked cells." 



" Tangential. This section is very satisfactory. The wood cells are long 

 and unmarked. The resin ducts are numerous, but scattered, the 

 cells being twice or three times as long as wide. In many cases they 

 are filled with or contain masses of dark material, representing the 

 resin now turned to a carbonaceous mass. 



" The medullary rays are composed of i , or in some cases of a 

 partially double, series of 2 to about 25 superimposed cells. They 

 are large and quite thick-walled. The average number of cells in 

 each ray is about 12" (Knowlton). 



According to Professor F. H. Knowlton, this species can hardly be dis- 

 tinguished from the existing S. sempervirens, of which he considers it 

 to be the ancestral form. 



Tertiary of the Yellowstone National Park, at Specimen Ridge, Fossil' 

 Forest at head of Crystal Creek, Fossil Forest on Cache Creek, etc. 

 (Knowlton). 



