PREFACE. 
V 
the species has taken place. It would require a 
new edition rather than a supplement, to indi- 
cate all of these changes, and any one who is 
conversant with the Genera as determined 
by Schreber and Willdenow, will readily com- 
prehend the principles on which these chan- 
ges have been made, and the characters of the 
new genera which have been adopted or pro- 
posed. Most of the alterations which have been 
made in American plants will be found in Nut- 
tall’s “Genera of North American Plants,” or 
in the valuable Flora of the Northern States 
now publishing by Dr. Torrey of New- York. 
If however the friends who have hitherto by 
their contributions added so much to the value 
of this work shall not find their patience ex- 
hausted; if they and if others who may be at- 
tracted to the study of this interesting science 
will continue to communicate to the author such 
plants as he may appear to have omitted, such 
as he may have inaccurately or imperfectly de- 
scribed, and will point out errors of any kind 
which he may have committed, he may hope at 
a future day to present this work in a form more 
worthy of their approbation. 
To those friends he feels gratified to make 
public his acknowledgements. With the late 
Dr. Muhlenberg of Lancaster, Penn, he was 
accustomed for many years to compare and 
collate the plants of Carolina and Pennsylva- 
nia, and derived from this correspondence 
