TO 



JOHN TORREY, LL. D., 



CORRESP. MEMBER OP THE UXKSAN BOCIETT. ETC., 



THIS VOLUME IS DEDICATED, 



IN G HATEFUL ACKNOWLEDGMENT 



OF THE FRIENDSHIP WHICH nAS HONORED AND THE COUNSEL 

 WHICH HAS AIDED 



THE AUTHOR 



FROM THE COMMENCEMENT OF HIS HOTANI^AL PURSUITS. 



Cambridge January 1, 1848. 



