iv INTRODUCTION. 



a number of papers which owe their existence to the discus- 

 sions which followed the publication of Mr. Darwin's " Origin 

 of Species," — discussions iu which Professor Gray took in 

 this country the foremost position. ^ 



It is not proposed to republish the works of descriptive 

 botany, although some of the early and most important of 

 these memoirs are out of print and quite beyond the reach 

 of the srreat mass of botanical students. The value of these 

 papers, however, is historical only, as all that they contain of 

 permanent usefulness has already been incorporated in stand- 

 ard works upon the science, or will be used in due time to 

 lighten the burden of those upon whom has fallen the task 

 of completing the " Flora of North America." There is even 

 less reason for reprinting any of the earlier editions of the 

 text-books. The last editions contain their author's latest 

 views upon the science, and are still within the reach of stu- 

 dents. Works of this character change necessarily as knowl- 

 edge increases, and the value of every edition of a text-book, 

 except the last, is merely historical. 



The philosophical essays, or the most important of them, 

 which grew out of the discussion of the Darwinian theory, 

 have already been republished by their author, and another 

 republication of these papers is therefore not proposed at this 

 time, although it is impossible, without having read them, to 

 understand rightly Professor Gray's influence upon the intel- 

 lectual movement of his time. 



There remain the reviews, the biographical notices, and a 

 few essays upon subjects of general interest to botanists. 

 They have long been out of print and have not been incor- 

 porated in any recent publication. It was believed therefore 

 that a reissue of these papers, or a selection from them, would 

 be a useful contribution to botanical literature, and a proper 

 tribute to the memory of their author ; and for these reasons 

 these volumes have been prepared. Many of the reviews are 

 filled with original and suggestive observations, and, taken 

 together, furnish the best account of the development of 

 botanical literature during the last fifty years that has yet 

 been written. 



