our colleagues. Especially to be mentioned here are the various Manuals and 

 Floras that cover to some extent plant species that occur in our region of investi- 

 gation. By way of acknowledgment and also as a ready reference, all of these 

 works that were consulted have been included in the Bibliography. We are most 

 grateful to have had these publications available to us. Since the subject matter 

 covered has been expanded to a considerable degree beyond the scope of that 

 of most past workers in this field, these ready references were especially helpful. 



We would like to note especially the work of C. D. Sculthorpe (1967), "The 

 Biology of Aquatic Vascular Plants." It is a most lucidly written treatise, and 

 one from which we have derived much help and information. A great amount of 

 pertinent and valuable information regarding these plants has been compiled in 

 this most useful work, and it is here highly recommended to all interested parties. 



Research on this project ran concurrently for several years with work on the 

 preparation of Correll's and Johnston's recently published (1970) "Manual of the 

 Vascular Plants of Texas." We are, indeed, grateful to our fellow-author of the 

 Manual, Marshall C. Johnston, of the University of Texas at Austin, and to the 

 many collaborators for the privilege of using in this work some parts of their 

 contribution to the Manual, where they and their individual contributions are 

 acknowledged. We are equally grateful to those individuals whose published 

 materials were adapted for use in the Manual, and acknowledged there, for the 

 use of some parts of their material in this work. Where new material has been 

 adapted for this work it is acknowledged where this adaptation occurs. 



There are many individuals, too numerous to mention by name, who have been 

 directly or indirectly helpful to us in our research, and to whom we are most 

 grateful. Foremost among these are the curators of various herbaria in which 

 specimens from our region are deposited. In regard to specimens, we wish to 

 acknowledge especially those that were received from several individuals who made 

 a special effort to collect aquatic plants for us. These are Frederick R. Gehlbach, 

 of Baylor University, who also joined us in some field work in Arizona, Jimmy R. 

 Massey, of Texas A&M University, Charles R. Hutchins, of Albuquerque, New 

 Mexico, and Elray S. Nixon, of Stephen F. Austin State College. We are also 

 grateful to Alan R. Smith, of the University of California at Berkeley, for his 

 having clarified for us a part of the difficult genus Thelypteris, and to Neil 

 Hotchkiss, now retired from the Patuxent Wildlife Research Center, U. S. Dept. 

 of the Interior, for his thoughtfulness in sharing his experience with us at the 

 beginning of this project, and for his continued interest in our work. 



Two botanists who accompanied us on field trips and were especially helpful 

 are Eugene C. Ogden, New York State Botanist, Albany, and Henry K. Svenson, 

 United States Geological Survey, now retired. 



In addition to help received from professional botanists, several highly skilled 

 amateurs in Texas have either directed us to new elements in our aquatic flora or 

 have provided assistance in one way or another. Among these are Geraldine E. 

 Watson of Silsbee, Peggy A. Amerson of Mt. Pleasant, Jim D. Bowmer of 

 Temple, and Raymond J. Fleetwood of Angleton. 



It is impossible to thank sufficiently the artists who have patiently and painstak- 

 ingly delineated the often intricate and complex species. We are especially indebted 

 to Vivien Frazier, with whom we have been associated in botanical art work for 

 many years, for her faithful attention to the most exacting details in the rendition 

 of her drawings. She has been of inestimable help to us. We are also grateful to 

 Jane W. Roller and Phoebejane Horning who prepared several of the drawings 

 used in this publication for works previously published by the senior author, and 

 to Regina O. Hughes, who previously made drawings for the senior author's 

 work on tuberous Solarium species of North America and Central America, for 

 several of her plates that were recently published in Clyde Reed's "Selected Weeds 



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