FLORA OF THE KOOTANIE FORMATION. 305 



tip when undistorted, but often from pressure become narrower at their 

 ends. Distortion from pressure often causes the segments to incHne 

 toward the ends of the leaf, and thus they seem to go off at an angle 

 smaller than the normal one with the midrib. Thej'^ are attached by 

 the entire width of their bases to the upper face of the midrib of the leaf, 

 so that the adjacent leases of the opposite segments are separated b}"- a 

 raised line. There is some indication that with age they become more 

 loosely attached to the midrib. At any rate the Geyser specimens show 

 numerous detached segments that have separated from the midrib along 

 this line. Detached segments are much more common than those borne 

 on the midrib. This deciduous character is marked in the Geyser fossils, 

 but is not noted by previous describers of this fossil. The frequent 

 detachment of the segments does not seem due solely to the accidents 

 of preservation. The width of the segments varies greatly, for some 

 leaves have only two segments on a side and others have the lamina on 

 each side of the midrib divided into numerous segments that are very 

 uniform in size and shape. Others have numerous segments, but they 

 varj'- greatly in width. In some cases the apparent segmentation, as 

 well as the shape, is due to pressure, the lamina splitting on the yielding 

 of the rock material. The width of the segments can not then be regarded 

 as a feature of any importance, and the same may be said of the number 

 of nerves, for that varies with the width of the segments. 



The nerves, although slender, are remarkably distinct. They are 

 always single, and when the segment is not distorted by pressure they 

 are strictly parallel. The pressure, however, has frequently narrowed 

 and sharpened the ends of the segments, and then the nerves are crowded 

 in the distorted portion. The nerves are described b}^ previous observers 

 as going off at right angles with the midrib, whereas in the Geyser fossils 

 the}^ rarely do so, but more commonly make an angle somewhat smaller. 

 In some of the figures given by Schenk they are represented as making 

 a much smaller angle. The nerves in their course to the ends of the 

 segments make a slightly sigmoid flexure, so that their tips are directed 

 slightl}^ forward. In the leaves distorted b}' pressure in the way men- 

 tioned before, this forward inclination is exaggerated. The' nerves are 

 thickened at the insertion of the segments on the midrib and the pressure 

 sometimes causes them to appear as raised lines on the surface of the 



MON XLVIII — 05 20 



