6 



seed or suckers beyond the limits of cultivated ground, 

 and likely to survive, unless destroyed by the agency of 

 man, are printed in small capitals. 



3. Italics have been reserved for introduced species 

 which have not become permanently established within 

 our limits. These adventive species range from plants 

 which have been found but once, like some of the wool- 

 waste Composit£e of Lowell and Chelmsford, to familiar 

 species, for example. Lucerne, which persists for many 

 years, but does not appear to thrive, and in a few cases 

 observed through a period of several years, has died out 

 altogether. Within this division, also, are included many 

 plants, such as the wool-waste Medicks, which spring up 

 in abundance every year ; it is not settled, however, 

 whether they are perpetuated by seed ripened in Middle- 

 sex and surviving the winter, or by fresh importations 

 from the original source. 



4. To facilitate the study of species not contained in 

 the Manual, either a description has been given, or 

 reference made to some volume of the Wood or Gray 

 series of text-books wherein such description may be 

 found. 



5. Whenever a plant is commonly met with in its 

 proper habitat, no location is given. Where several 

 stations are given without comment, the species will 

 probably be found more Avidely distributed. The occa- 

 sional presence of a plant in stations besides those men- 

 tioned is indicated by the abbreviation et al. 



6. Wherever the "Manual" is mentioned, reference is 

 made to Gray's Manual, 5th edition, unless otherwise 

 designated. 



7. In the Phanerogams and Vascular Cryptogams, an 

 asterisk indicates that no specimen of the plant so desig- 

 nated is in the county herbarium. It does not follow, 

 however, that such species are always rare. 



