34 HARPER 



onomic groups, such as species, though the latter are mutually 

 exclusive categories and the former often are not. For instance, 

 both are capable of being discovered, described, named, and 

 associated with certain type-localities. Records of both may be 

 preserved by descriptions, photographs, measurements, and other 

 means. Both have their diagnostic characters, with more or less 

 variation and intergradation. Both have passed through pro- 

 cesses of evolution, are self -perpetuating, and are liable to dis- 

 appear through geological or climatic changes of the works of 

 man. New ones may also originate, suddenly or gradually. Both 

 have more or less definite geographical distributions and regions 

 of best development. Both are capable of being subdivided, 

 combined, or relegated to synonymy, with the increase of our 

 knowledge concerning them. Habitat-groups, like species, can 

 also be aggregated into larger categories, analogous to genera 

 and families. 



In the following pages about twenty different habitat -groups 

 •or kinds of plant-communities are described and analyzed. These 

 it is believed will cover something like 99% of the area under con- 

 sideration. There are several other kinds of plant-communities 

 in the region, but they are rare and as yet imperfectly understood, 

 and it seems scarcely worth while to describe many of them 

 from single examples, without knowing their variations, any 

 :more than a new species should be described from a single 

 specimen. Some of them when better known may be described 

 in future editions. 



The accompanying map (fig. 1) shows the actual relationships 

 on the ground of twelve of the principal habitat-groups in an 

 imaginary typical portion of the Altamaha Grit region. It is 

 more or less conventionalized and does not pretend to show the 

 relative area of each. The names used will be explained farther 

 on, when the groups are discussed individually. It is quite 

 possible to give technical names to these groups, as well as to 

 plants, as Dr. Clements has shown, 1 but in order to do this new 

 names would have to be coined for most of them, a task which 

 may well be left to future investigators. 



1 See Olsson-Seffer, Bot. Gaz., 39: 187-193. March, 1905. 



