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 the 

 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 type 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 types 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 t^'jDe 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 plants obtain both a fair idea of the species of plants from 

 any particular region and some knowledge of the tyj^e or types 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 the 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 are 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 chara( ter of the vegetation. 



