ACKNOWLEDGMENT. 
In the foregoing pages, the writer has endeavored to give 
proper credit to those who have contributed towards extending 
the size of the flora, or a knowledge of the distribution of the 
species. But other assistance has been rendered him by per- 
sons not directly interested in the local character of the work 
which should not pass without an acknowledgment. He is 
indebted to Prof. Asa Gray, Prof. G. L. Goodale, and Prof. 
Sereno Watson of the Cambridge herbarium, for much valuable 
assistance during the past five years in identifying many dif- 
ficult species of plants; to Prof. W. G. Farlow, for many 
kindnesses in determining the lower cryptogams; to Prof. 
T. P. James, for similar services regarding the mosses; to 
Prof. C. S. Sargent, for much information of value concerning 
the trees and shrubs, and to Mr. Chas. J. Sprague, not only 
for his contribution of the entire list of lichens, but also for 
kindly remembering to communicate any rare plant found while 
collecting in Essex county. 
The writer also desires to express his obligations to Messrs. 
Edwin and Charles E. Faxon, for their kindness in revising 
the final proof, and to Mr. Woodbury P. Conant, for his as- 
sistance in preparing the index. 
12 (177) 
