198 THE FORMATION 



in addition to the name, date, and place of collection, the phyad or vegeta- 

 tion form, the geographical area, the rank of the species, the aspect, and 

 the formation. To these may well be added data concerning migration 

 contrivances, seed production, pollination, period of flowering, etc. The 

 photographs are mounted on the usual herbarium sheets, and placed in the 

 proper order in the various groups, and a similar disposition is made of 

 quadrat and transect charts, and such physical factor summaries as seem 

 desirable. 



246. Succession herbaria. The arrangement of formation herbaria may 

 follow the classification of formations with respect to character, region, or 

 development. The first is the most convenient for purposes of instruction, 

 and has distinct advantages in permitting a close comparison of the vegeta- 

 tion of different habitats. The second basis, which is the one used in the 

 Herbaria Formationum Coloradensium, is peculiarly adapted to mountain 

 vegetation in which the zones are usually very distinct. The arrangement 

 of herbaria in a developmental series, however, is the most logical and the 

 most illuminating, since 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. Indeed, 

 the latter should be made mferely the starting point for these in all regions 

 where the causes which bring about successions are active. Where weather- 

 ing 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. 

 After a formation herbarium of each stage has been made in the way in- 

 dicated, a succession herbarium is obtained merely by arranging the various 

 herljaria in the sequence of the developmental stages. Thus, in the Colo- 

 rado collection, the subalpine formations are arranged according to altitude 

 in the following series: (i) the pine formation, (2) the gravel slide for- 

 mation, (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 indicate the development 

 of the spruce-pine forest by arranging these five formations in their proper 

 order in a succession herbarium, as follows: (i) the gravel slide formation, 

 (2) the half gravel slide formation, (3) the pine formation, (4) the bal- 

 sam-spruce formation, (5) the spruce-pine formation. 



