2 PUBLIC HEALTH BULLETIN NO. 2 86 



The higher plants ordinarily are made up of roots, stems, leaves, 

 and in proper season flowers or fruits. Each of these presents itself 

 in the widest diversity of form and habit, and each is on occasion 

 lacking in some species. In most cases vegetative characters have 

 been used in the keys, as these characters are always present and are 

 best understood by the non-botanist. In some instances, however, 

 floral characters must be used to make clear separations in the keys. 



The keys have been compiled from a variety of sources and have 

 been tested in the field and from herbarium material. They are of 

 the non-indented dichotomous type as this type is most economical 

 in printing. In each case two alternatives are offered, one of which 

 should fit best the plant in hand. The basis of the primary divisions 

 of the key is the growth habit of the plant. This means of division 

 is used because the habit of the plant has an important relationship 

 to its importance as harborage for mosquito larvae. Divisions in the 

 key are made in as great measure as possible on vegetative characters 

 as the layman is usually unfamiliar with the anatomy of the floral 

 organs. An illustrated glossary of both vegetative and floral char- 

 acters opens the way to a fuller working knowledge of the keys. 



Desirable tools are a hand lens of about 10 magnifications and a 

 millimeter scale, as in some cases details which require magnification 

 are used in separating the species, and in many cases comparative 

 size is used. It is suggested that if in the process of using the key 

 some character seems ambiguous, the plant be looked for in both 

 divisions. If after keying and comparison wuth the illustrations there 

 is still doubt as to the identity of the plant, it should be checked 

 with the more adequate descriptions of the larger manuals. 



Each genus of the main key is illustrated by a drawing of a repre- 

 sentative plant. The majority of these have been prepared especially 

 for this guide by Garnet W. Jex, United States Public Health Service, 

 but a large number have been borrowed from several publications. 

 The author-source of these borrowed figures has been acknowledged 

 elsewhere. 



The nomenclature used in this guide is conservative and follows 

 the best present day usage. In many cases the scientific names differ 

 from those used by Small in his Manual of the Southeastern Flora, 

 and in most places these discrepancies have been noted in the text. 



Roots are used in the keying in only a few instances. Stems are 

 not widely used except in the primary divisions of the keys. Whether 

 the stem is woody or herbaceous is of great importance but is usually 

 obvious. The habit of the stem, whether erect or reclining, lax or 

 rigid, is also important, as is the presence or absence of hairs or other 

 appendages. 



Leaves show great diversity in many characters. The shape is 

 perhaps most important. The state of division of the leaf, whether 



