of the United States" (1970), and several plates of Hibiscus. We are most grateful 

 for the privilege of using some of the grass spikelet drawings by Agnes Chase, 

 published in Hitchcock and Chase's "Manual of the Grasses of the United States" 

 (1935, 1951). We are grateful for the privilege of using drawings of several 

 orchids by Blanche Ames Ames and Gordon W. Dillon, and of several species of 

 Umbelliferae by Mildred E. Mathias. To the various artists whom we have not 

 known personally but whose work we admire and are grateful to include in our 

 publication, we extend our most sincere thanks. These are Mary Wright Gill and 

 Edna May Whitehorn who made most of the drawings published in Hitchcock 

 and Chase's grass manual; Mary Barnas Pomeroy, Patricia Verret Reinholtz, 

 Robert Mill and Emily Patterson Reid, who prepared the drawings published in 

 Mason's "A Flora of the Marshes of California" (1957); Barbara N. Culbertson 

 and M. Grady Reinert, who prepared the drawings for Godfrey's yet unpublished 

 research on the aquatic and marsh plants of Florida. We are, indeed, grateful to 

 each of these individuals for his or her contribution to this project. 



The careful and exacting work of Mrs. Aileen Maddox in typing the manuscript 

 and her assistance in all other phases of the research we gratefully acknowledge. 

 Her enthusiasm for the project frequently lifted our sagging spirits. 



As noted before, the main purpose of this work, as is that of any such manual, 

 is to provide a means for the identification of the aquatic and wetland plants in 

 the region under consideration; namely, southwestern United States. For the most 

 part, we believe that the text is uncomplicated and straightforward and needs no 

 explanation. Several points, however, should be clarified. Although the families 

 are arranged phylogenetically essentially in accordance with the Engler and Prantl 

 System, many of the genera and the species within a family or genus, respectively, 

 are not arranged in phylogenetic order. This phase needs more study than time 

 allowed for the present. In the Keys the first number in each couplet, except for 

 the first pair, is accompanied by a number in parenthesis. This number in paren- 

 thesis refers back to the previous couplet from which the present one was derived. 

 With this aid one can quickly and readily retrace one's steps back to the very 

 beginning of the Key if need be. The branches or "legs" of each couplet are 

 terminated either by a plant name or by a number in parenthesis that refers to a 

 subsequent couplet. In regard to the measurements and numbers of parts given 

 in some sections of the text, as "petals (5-) 7-9 (-12) mm. long," such may be 

 interpreted as "petals usually 7-9 mm. long but sometimes as short as 5 mm. or 

 as much as 12 mm. long." TTie less common extremes in measurements and 

 numbers of parts are enclosed in parentheses. 



We can not over-emphasize the need for exerting the most strenuous effort 

 to clean up our total environment. Our close observation of much of the aquatic 

 and wetland habitats in southwestern United States has indelibly impressed upon 

 us the appalling conditions that now exist in many of these places that are of Vital 

 interest to plants and animals, and to the general well-being of mankind. Along 

 with the present cleaning, and the future protection, of our environment will 

 come conservation. One follows the other! 



Finally, we believe that any kind of work such as ours should represent a 

 combination of our efforts and those of our many colleagues. We are grateful 

 for their work which has contributed immensely to the fulfillment of the present 

 task. 



Donovan S. Correll 

 Helen B. Correll 



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