294 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
resort to the collection of plants in the various herbariums and to the 
lists of plants published in various books and journals; in this way 
the distribution of the plants is discovered, the knowledge of which 
is valuable both to the taxonomist and the biologist. In this method 
the research worker must either for himself consult all the plants in 
the herbariums and represented in the lists and must verify their 
identification or else depend for their value upon the person identify- 
ing the plant or publishing its name. It is not necessary to see thft 
plant growing. The species are all units and are well represented as 
such by mere names. 
In using the second method of comparative study, that of consider- 
ing types of vegetation, one encounters a very different proposition. 
Types represent groups of plants and groups which do not necessarily 
consist of separate species, in fact a tyj^e of vegetation may be made up 
of a number of species. Types of vegetation, then, can be represented 
only very indefinitely by published lists of names of plants or by the 
plants themselves as they occur mounted on herbarium sheets. It is 
true that names are in use to designate certain t;yiDes of vegetation, 
terms such as xerophyte, hydrophyte, mesophyte, and others of more 
restricted meaning; and it is certain that these terms picture to one 
at all familiar with such work definite features in the vegetation. 
Moreover, the characteristics of any type of vegetation are often so 
well shown in the species constituting that type that one can by ex- 
amining herbarium specimens very commonly determine to what type 
of vegetation the plant in question belongs. 
So far it may be seen that one can by research among collections 
and lists of jilants obtain both a fair idea of the species of plants from 
any particular region and some knowledge of the t}']:)e or t\^5es of 
vegetation found in that region. So much can be done at home. The 
types, however, represent groups, and as the groups are often com- 
posed of many species which have one feature in common but often 
have a wide range in size, outline, method of branching, and color, 
it is impossible to give a complete and at all real picture of a locality 
without considering these various features, characteristics which can 
be ascertained only by traveling among tlie regions in question and 
by viewing personally the types of groups or composites of species 
as they are growing together in the various localities. The modifica- 
tions of groups arc so great that it is necessary to visit many localities 
and to visit the same localities at various times of the year before one 
can obtain a true knowledge of the character of the vegetation. 
