770 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



four. The ducts occupy nearly one-half of the area, thus producing an 

 open, soft wood. The longest series of ducts, embracing 10, is 0.50 mm. 

 in length. Series of 4 or 5 having a length of 0.30 mm. are common. 

 The small single ducts are 0.05 to 0.07 mm. in long and 0.0-4 to 0.05 mm. 

 in short diameter. The average short diameter of all ducts is about 0.07 

 or 0.08 mm. 



The wood cells are arranged in distinct radial rows. Thev are rather 

 large and thin-walled, also showing that the wood was a soft, porous one. 



The medullary rays in this section are rather numerous. The}' are 

 2 or sometimes 3 cells wide, and the cells are short and thin-walled. 



Radial section. — The ducts appear especially numercms in this section. 

 The marking on the walls is rather obscure, but they seem to be uniformly 

 provided with minute pits. 



The rays form high plates of short, thin-walled cells, apparently with 

 small circular or oblong pitlike markings. 



The wood cells are very long. They have sharp-pointed extremities 

 and thin walls. 



Tangential section. — This section is vei'v characteristic, the most prominent 

 feature beino- of course, the cut-off ends of the medullary rays. The rays 

 are various, being 2 or rarely 3 or 4 layers of cells wide. The number of 

 vertical rows is very indefinite, being rarely less than 10 or more than 30. 

 The cells are rectangular, beino- often twice as long- as wide. Some of the 

 cells in the middle of the ray are more or less irregular in shape. All are 

 very thin-walled. 



The wood cells are the same as in the radial section. 



The ducts are also prominent. They have oblique partitions and the 

 walls are provided with round pits. The markings on the walls are not 

 different from those to be observed in the radial section, but they happen to 

 be better preserved. 



In my original MS. this form was described under the new generic 

 name of Populoxvlon, from its undoubted close resemblance to wood of 

 living Populus. It is with some hesitation that I transfer it to Felix's 

 species, for they do not agree in every particular - . On the whole, howeA*er, 

 it is more than probable that they are the same, and I have so regarded 

 them The generic diagnosis, based upon the wood from the Park only, 



