PART I- -ANATOMY 



INTRODUCTION 



The present work had its origin in 1880, in an attempt to con- 

 struct a system of classification for the North American Coniferse 

 based upon the anatomy of the vascular cylinder of the mature 

 stem. The fundamental idea was that such a classification would 

 prove of great value in the identification of material used for 

 structural purposes, but investigations had not been carried very 

 far when it became manifest that some such arrangement was 

 imperatively demanded in other directions and for purposes of 

 a more strictly scientific character. In entering upon the study 

 of fossil plants it was recognized that the most fruitful source of 

 reliable data must be found in the stem structure. At that time 

 there was little in the way of an adequate basis for further study 

 of this sort, inasmuch as the current diagnoses of the vascular 

 structure were found in most cases to be singularly inadequate, 

 and often so incorrect as to require extensive revisions. It was 

 found furthermore that in order to reach correct conclusions in 

 the case of stems which must often present marked structural 

 alterations, arising through the influence of decay and other con- 

 ditions attending fossilization in its various forms, it was indis- 

 pensable that there should be a trustworthy means of comparison 

 with existing types, whereby sources of error arising from elimi- 

 nated structures might be definitely excluded, and the fossil 

 referred with certainty to its nearest relative. The original 

 intention was therefore modified with a view to meeting the 

 requirements of paleobotanical research. During the time these 

 investigations have been in progress there has been much change 

 in the views held by botanists respecting the significance of ana- 

 tomical features as affording evidence of descent; and our own 



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