PREFACE ix 



from December, 1903, to March, 1904, I examined the littoral 

 flora of the west side of South America at various localities 

 between Southern Chile and Ecuador ; and finally completed 

 this investigation by comparing the shore-plants on the Pacific 

 and Atlantic coasts of the isthmus of Panama. Returning to 

 England with a fresh collection of data, I passed many months 

 in elaborating and arranging all my notes, waiting vainly for a 

 clue to guide me in framing a scheme by which I could bring 

 the results of many years of work into some connected form. 

 At last I decided once again to take the floating seed as my 

 clue, and without any prearranged plan I allowed the work to 

 evolve itself. Now that it is finished, I can see some obvious 

 defects ; but if any other plan had been adopted I scarcely 

 think that I should have been more successful in piecing 

 together in a single argument materials resulting from so 

 many years of research and relating to so many aspects of 

 plant-life. 



Yet the final object of a naturalist would be but a sorry one, 

 if his aim were only to write a treatise and append his name to it. 

 His personal faith lies behind all his work ; and no one can pursue 

 a long line of study of the world around him without rising from 

 his task with some convictions gained and some convictions lost. 



As far as the observation of Nature's processes at present in 

 operation can guide us, the world presents itself to us only as a 

 differentiating world. We can perceive, it is true, a progressive 

 arrangement of types of organisms from the lowest to the highest, 

 and we can perceive a development of varieties of the several 

 types ; but the only process evident to our observation is that 

 concerned with the production of varieties of the type. Nature 

 does not enlighten us as to the mode of development of the type 

 itself. We can, for instance, detect in actual operation the process 

 by which the different kinds of bats or the different kinds of men 

 have been developed ; but there is no principle in Nature evident 

 to our senses that is concerned with type-creation. Though we 

 can supply it by hypothesis, we cannot discover it in fact. On the 

 other hand, the evidence of differentiation is abundant on all sides 

 of us, both in the organic and in the inorganic worlds. The history 



