770 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



tour. The ducts dci-upv uearlv oue-hnlt' of the area, tlui.s jiiixhiciug au 

 open, soft wood. Tlie lonij-est series of ducts, enibr;ieiny 10, is ().5() mm. 

 in length. Series of 4 or 5 liaving a length of 0.;>() mm. are eommon. 

 The small single duets are O.O.") to 0.07 unn. in long and 0.04 t<i (t.Oo mm. 

 in short diameter. The average short diameter of all duets is aliout 0.07 

 or O.OS mm. 



The wood cells are arranjied in distinct radial rows. The"\' are rather 

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



The medullarv ravs in this section are rather numerous. They are 

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



Radial section. — Tlic ducts appear especialh" numerous in this section. 

 The marking on the walls is rather oliscure, hut tliev seem to l)e unifonnlv 

 provided with minute pits. 



The raA's form high plates of short, thin-walled cells, apparently with 

 small circular or oblong pitlike markings. 



The wood cells are verv long. They have sharp-jxiinted extremities 

 and thin walls. 



Tangential section. — Tlils sectlou Is A'erv cliaracteristic, the most prominent 

 feature being, 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, being 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 ju-e the same as in the radial section. 



The <lucts are also prominent. Thev liave oblique partitions and the 

 walls are ])rovided with round ]iits. The markings on the walls are not 

 different fi-om those to he observe(l in tlie radial section, but they happen to 

 lie better preserved. 



In niv original jMS. 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 ti'ansfer it to Felix's 

 species, for the\' do not agree in every particular. On the whole, however, 

 it is more than probable that they are the same, and 1 have so regarded 

 them The generic diagnosis, leased upon the wood from the Park oidv, 



