SINCE this Memoir was in print, the travels of Lietit.-Colonel 

 N. Prejevalsky in Mongolia have appeared. 



The Eussian explorer penetrated into the province of Kan-su, 

 and while there ascertained beyond doubt that the true rhubarb 

 of commerce was Rheum palmatumj and not Rheum qfficinale, 

 as had been supposed. The passage therefore relating to the 

 identification of the plant cannot stand good. 



Thanks are gratefully offered to the Linnean and Pharma- 

 ceutical Societies for permission granted to republish many 

 of these papers ; to the Secretary and Librarian of both 

 Societies for their kind assistance ; and to Dr. Hooker for 

 the loan of a valuable private manuscript. 



