lla. 
keys were modified to exclude species having a strictly Piedmont 
distribution and those restricted to habitats which do not occur at 
the Chesapeake Bay Center. Entirely new keys were prepared for some 
of the more complex taxa which have limited representation at the Center. 
There are two reasons for any similarities present between keys 
in the literature cited above and keys in the checklist. First, the 
dependability of the characters in the keys in the literature. Second, 
the need of a framework to facilitate the anticipated periodic revision 
of the keys as additional species are collected. Such revisions will 
be accomplished more readily if the organization of the checklist keys 
is designed to allow for them. 
Therefore, when a couplet in one of the keys in the literature 
separates a genus or species which has in fact been collected at the 
Center from one not yet discovered there but expected to occur in the 
vicinity, both halves of the couplet are included in the checklist key 
but the word "expected" follows the unused half and the taxa to which 
it refers are named in parentheses. This practice appears justifiable 
in view of the continued investigations to be conducted at the Center 
and the rich and fluctuating flora of the surrounding county, described 
by Stieber (1967). Stieber notes a great intermingling of northern, 
southern, and introduced species, the whole assembly subjected to wide- 
spread human disturbance. From field collections west of the Chesapeake 
Bay Center and an examination of the District of Columbia and Vicinity 
collection in the U. S. National Herbarium, Stieber has compiled a 
checklist of 647 vascular species for the county. His list cites 316 
