FORMATION AND SUCCESSION HERBARIA 197 
244. Details of collecting. Formational collections, unlike the ordinary 
sets of exsiccati, can not be made upon the first visit to a region, or by 
a single journey through it. The determination of formation limits, and 
of developmental stages, of aspects, layers, abundance, etc., must necessarily 
precede, a work which alone takes several years. Moreover, collecting itself 
requires more than one year in a region containing numerous formations. 
This is exemplified by the Herbaria Formationum Coloradensium. The 
preliminary study for this was made from 1896-1899, the collecting was 
done chiefly in 1900 and 1901, while additional numbers were added in 
1902-3. For the purposes of the formation herbarium, specimens should 
be collected and pressed in such fashion as to show all the ecological fea- 
tures possible. Plants must be collected both in flower and in fruit, with 
the underground parts as perfect as may be. Seedlings and rosettes should 
be included whenever present. In pressing, one or two leaves should be 
arranged with the lower side uppermost to admit of the ready comparison 
of both surfaces. Opened flowers are valuable for flower biology, while 
seeds and fruits are desirable for showing migration contrivances. The 
ferns, mosses, and lichens of the formation should be fully represented, to- 
gether with the more important fungi and algae. The number of photo- 
graphs taken for each herbarium should be limited only by considerations 
of time and expense. The ideal series consists of a general view of each 
formation, showing its physiographic setting, nearer views of each of its 
aspects, detail views of its consocies, societies, and layers, and flower portraits 
of all the constituent species. Such a series can only be obtained by resi- 
‘dence through a long term of years, and in most cases general and aspect 
views, with portraits of the facies and a few of the striking principal 
species, must suffice. Quadrat and transect charts, together with forma- 
tional maps, are extremely desirable, and, indeed, all but indispensable. 
245. Arrangement. The arrangement of species within each formation 
herbarium is based upon the structure of the vegetation. The primary 
groupings are made with reference to time of appearance and abundance; 
when definite zones, associations, or layers are present, they must likewise 
be taken into account. In the Colorado collection, the first division is into 
three aspects based upon the period of flowering (aspectus vernalis, aesti- 
valis, autumnalis). Within each aspect, the species are arranged with re- 
spect to abundance in the groups, facies, principal species, and secondary 
species. Each group is placed in an ordinary manila cover, which bears a 
printed label indicating the aspect and the group. The species labels g’ve, 
+Clements, F. E. and E. S. Herbaria Formationum Coloradensium. 1902. 
