HOFFMANN: FLORA OF BERKSHIRE COUNTY. 175 



with the accompanying statement of habitat; thus, "Rich woods; 

 common," impUes that the species is infrequent or entirely absent 

 except in rich woods. Moreover, the term "common" cannot be 

 used with anything like mathematical precision. A species may be 

 so designated if it occurs in fairly large munbers wherever the condi- 

 tions are suitable, but owing to its association with a number of other 

 species struggling for space in the same environment the total number 

 of plants in a given area may not be nearly so great as in the case of a 

 species which crowds out all competitors. "Frequent" means that 

 the species may be found without much search but that there are areas 

 in many apparently suitable localities where it is absent. "Occa- 

 sional " and " rare " explain themselves. When a plant is " occasional " 

 or "rare," all the stations where it has been found have been given. 

 The term "local" is used when a species is common at a few stations. 



Since the publication of the Manual a number of new species and 

 varieties have been described, or the treatment of species or groups 

 has been revised. Brief descriptions of these new species, varieties, or 

 forms have been included in this list, generally copied from the original 

 description, so that the list may supplement the Manual for the region 

 which it covers. 



All varieties and forms have been given a separate paragraph for 

 convenience in using the list, instead of combining subordinate varie- 

 ties and forms in the same paragraph with the species. 



In a very few instances only, liew combinations have been made in 

 this list. A few combinations treated in the Manual as varieties have 

 been reduced to forms, in accordance with the more recent treatment 

 of these phenomena. The incised, or auricled forms of ferns, color 

 phases of fruit or flower, which occur with the typical form and are 

 not combined with any other character or any marked difference in 

 range are treated as forms. A few color forms, most of which have 

 been well known to collectors, but have not yet received a name, have 

 been given names in this list. A list of all new forms and combina- 

 tions is given in the Appendix. 



Artificial keys for the determination of species in large and difficult 

 groups are an essential feature of the standard manuals of botany. It 

 has seemed to the author unnecessary to furnish the present work 

 with such keys, except where the number of species found in Berkshire 

 County is much smaller than the number covered by the manuals. 

 In such cases keys covering only the species known to occur in Berk- 



