VI PREFACE 



inclusion of paleobotanical material. Aside from a far more com- 

 plete knowledge of the living groups, including as it does now at least 

 the salient facts in reference to almost every genus, there have been 

 two notable advances. In the first place, during this period vascular 

 anatomy has developed as a subject of first importance, and some of 

 its most conspicuous contributions have been in connection with the 

 origin and relationships of gymnosperms. In the second place, 

 paleobotany has brought to light during the last decade more facts 

 of importance in reference to the history of gymnosperms than in 

 reference to any other group of plants. This has enabled us to treat 

 of the extinct groups in a way that was impossible ten years ago. 



Attention is called to the fact that on the basis of new knowledge 

 we have reorganized our presentation of the gametophyte, by recog- 

 nizing the spore as its first cell, rather than the mother cell, as in the 

 previous volume. This needs no explanation, as it seems clear that 

 the sporophyte generation ends and the gametophyte generation 

 begins with the appearance of the spore. The plan of grouping the 

 special literature of each great division in chronological order at the 

 end of its presentation, and the general literature of gymnosperms 

 in alphabetical order at the end of the volume, is continued. Such 

 illustrations as have been copied are not only credited, but also referred 

 to the publications in which they first appeared. 



The authors appreciate, perhaps more keenly than anyone, that 

 a book of this nature in a certain sense is out of date as soon as it has 

 left the press. Papers will continue to appear which would have 

 been of great service in this volume, and yet perhaps no great group 

 of plants is just now in better condition for a presentation which 

 professes to be only a concise summary of knowledge, useful in 

 stimulating and guiding further research. 



~ John M. Coulter 



Charles J. Chamberlain 



The University of Chicago 

 May 19 lo 



