Xll PREFACE. 



have not only marked the accented syllable, but have followed Loudon's 

 mode of indicating what is called the long sound of the vowel by the 

 grave ( x ), and the short sound by the acute accent-mark ('). In respect 

 to this, my friend, Ml!. Folsom, has obligingly rendered most important 

 assistance throughout the pages of this volume. 



The imperative necessity of economizing space to the utmost, alone has 

 debarred me from more largely recording my acknowledgments to nu- 

 merous obliging correspondents, in all parts of the country, who have con- 

 tributed to this work, either by notes of corrections, observations, or cata- 

 logues, or by communicating specimens of rare or local plants. In the 

 comparison of our flora with that of Europe, I am greatly indebted to my 

 excellent friend and correspondent,. M. Godet of Neuchatel, author of 

 the Flore du Jura, for a suite of authentically determined plants of that 

 district, and for a series of acute and very important critical notes upon 

 many of our own identical or related species. 



As to special collaborators in the preparation of the work, in addition to 

 the acknowledgments made in the preface to the former edition, I have 

 again to express my particular indebtedness to my friends, John Carey, 

 Esq., now cf London, for various emendations in the genus Carex, formerly 

 elaborated by him for this work ; and Dr. Engelmann of St. Louis, for 

 full notes upon the botany of our Western borders, many critical obser- 

 vations upon various genera, and for contributing the articles upon Cus- 

 cuta, Euphorbia, and the three genera of Alismece. The renewed and 

 still more extensive contributions of Mr. Sullivan r have already been 

 referred to, — •contributions which introduce a new era in the study of 

 American Muscology, and which justly claim, not only my warm per- 

 sonal acknowledgments, but the in-atitude of all the votaries of our science 

 in this country. 



I renew the request, that those who use this book will kindly furnish 

 information of all corrections or additions that may appear to be necessary, 

 so that it may be made more accurate and complete in a future edition. 



Harvard University, Cambridge, 

 June &0ih, 1858. 



