416 Systematic Paleontology 



'"'' Microscopic analysis. — Transverse section : The fragments are all too 

 small and too poorly preserved to show the annual rings to the naked 

 eye, but under the microscope they are observed to be tolerably distinct. 

 The ring of fall wood consists of from three to six or eight compressed 

 cells in each radial row. The spring wood contains some very large 

 cells, with a diameter in some instances of .062 mm. The number of 

 cells in each row of tracheids varies according to the width of the 

 annual ring, there being frequently as many as one hundred. Large 

 intercellular spaces occur particularly where additional rows of tracheids 

 have been introduced. 



" Radial section. — In this section the tracheids are shown to be provided 

 with one row; or, in some rare instances, with two longitudinal rows 

 of bordered pits. They occupy the center of the cell and are close to- 

 gether, almost touching in some cases. The larger have a diameter of 

 .020 mm., and the smaller a diameter of .015 mm. The medullary rays 

 consist of typical parenchymatous tissue. The individual cells are 

 short, covering the width of from four to eight tracheids. I have not 

 been able to detect markings on the walls of the rays, but this may 

 be on account of the poor state of preservation of the specimens. The 

 resin ducts are 'not numerous. They are of nearly the same size and 

 shape as the tracheids, and in fact look very much like tracheids with 

 transverse partitions. They are almost always empty. 



'"'' Tangential section. — The tracheids are not provided with pits on the 

 tangential walls, or at least none have been detected. The medullary 

 rays in many cases are two cells broad, and, as above indicated, from 

 one to thirty-five cells high. The individual cells of the rays have a 

 diameter of from .017 mm. to .030 mm." — Knowlton, 1889. 



Additional and somewhat better preserved material enables the writer 

 to add one or two features to the foregoing description. It may be 

 noted that the so-called annual ring is not distinct in the present section, 

 where, over a distance of 2 cm., there is but a single zone of smaller 

 cells. This is only three or four cells wide and not at all regular. It 

 undoubtedly denotes a slackening of vitality but hardly merits the term 

 of fall wood. The radial rows of tracheids are somewhat irregular and 



