Preface v 



A difficult portion of my problems has received the sympathy and aid of the 

 Department of Marine Biology of the Carnegie Institution of Washington, and 

 its Director, Dr. A. G. Mayer, has spared no pains and expense in the attempts 

 to stock with alien races the coral islands of the Tortugas and Marquesas groups 

 in the effort to learn, by experiment in nature, something of the laws of evolu- 

 tion, by dispersion, isolation, and changed environment. 



It is also a pleasure to acknowledge the helpful and loyal aid received from 

 many others in the progress of this investigation, and especially I am indebted 

 to Dr. J. K. Breitenbecher and Mr. J. G. Sinclair for enthusiastic aid in the 

 Tucson experiments. 



That portion of the project which from 1904 to 1910 was conducted in the 

 tropical regions of Mexico, and especially in the rain forests of Vera Cruz, has 

 been materially aided by many friends in that country. Especially I am in- 

 debted to the late James Parkin, of the Hacienda Motzorongo, and to his admin- 

 istratores, Senor P. Eandolph and Senor I. P. Lorio, for valuable aid in much 

 of the transplantation and acclimatization experiments in the rain forests of 

 Vera Cruz. These friends and the patient, loyal Indian helpers and packers 

 made possible a series of complex experiments in the midst of a virgin tropical 

 rain forest. 



In the preparation of tlie material for publication, much of the reduction of 

 data and compilation of the tables has been done by Miss Edna Scott. The 

 drawings in color, the colored photographs, and all of the prints of negatives 

 taken in the field, as well as the text illustrations, have been prepared by 

 Mr. K. Toda. 



To these friends and to many others I am under obligations for many kindly 

 acts in aid of this investigation, which have been contributed to its good points, 

 but to me must be charged that which proves to be error or misdirected effort. 

 No finality is expected and I shall feel that my efforts have not been in vain if 

 either data or hypotheses serve to stimulate further advances or help to correct 

 present misconceptions. 



William Lawrence Tower. 



Desert Botanical Labobatobt, 



November 1, 1916. 



