4 Frederic E. Clements 



printed label indicating the aspect and group. The species labels 

 give, in addition to the name, date, and place of collection, the 

 vegetation form, the geographical area, the rank of the species, 

 the aspect, and the formation. The labels are printed in Latin, 

 and the whole nomenclature is of necessity in this international 

 language. The terms used are those proposed by the writer in 

 "A System of Nomenclature for Phytogeography." 



The arrangement of formation herbaria may follow the classi- 

 fication of formations with respect to character, region, or devel- 

 opment. The first is certainly the most convenient for purposes 

 of instruction, and has distinct advantages in permitting a close 

 comparison of the vegetation of different habitats. The second 

 arrangement, which is the one followed m the "Herbaria Forma- 

 tionum Coloradensium," is peculiarly adapted to mountain vege- 

 tation, in which the zones are usually very distinct. The arrange- 

 ment of herbaria in a developmental series, however, is at the same 

 time the most logical and the most illuminating, as the structure 

 of the ultimate formations is not only made plain, but the stages 

 in their development are also laid bare. Such succession herbaria 

 are the natural outgrowth of formational ones. The latter, in- 

 deed, should simply be made the starting point for the former in 

 all regions where the causes which bring about successions are 

 •active. Where weathering is still an important factor, as in 

 mountains, the initial and intermediate formations which lead to 

 the final grassland or forest are often in evidence, and the group 

 of formation herbaria may be changed into a succession herbar- 

 ium simply by arranging them in the sequence of the develop- 

 mental stages. Thus, in the Colorado collection, the subalpine 

 formations are arranged according to altitude in the following 

 series: (i) the pine formation, (2) the gravel slide formation, 

 (3) the half gravel slide formation, (4) the aspen formation, (5) 

 the balsam-spruce formation, (6) the spruce-pine formation, (7) 

 the meadow thicket formation, (8) the brook bank formation. 

 Of these, five belong to the same succession, and it is possible to 

 trace the development of the spruce-pine forest by arranging 

 these five formations in their proper order in a succession her- 



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