27 
Fundamental Units of Vegetation. 
by the term “ formation,” and although many other terms have been 
used to convey the same general idea, and the term has been used 
to denote other concepts, yet the original term of Humboldt, and in 
the general sense used by Humboldt, meets with wide acceptance 
at the present time. It is true that Humboldt’s concept has been 
expanded, as he appears to have had no notion of uniting allied 
associations into a group of wider significance ; but such a classifica¬ 
tion of associations was ultimately inevitable. It appears likely 
that the term association, in the general sense here indicated, will 
be submitted for adoption at the International Congress of Botanists 
shortly to be held at Brussels; and one hopes that its adoption will 
be effected. A firm if small step will then have been taken in the 
direction of the unification of the use of phytogeographical terms ; 
although the precise degree of relationship between the formation 
and its associations may not be fully realized for some time to come. 
The Plant Formation. 
The concept of the plant formation is, in a general way, much 
older than the term; for whilst the latter only dates from Grisebach 
(1838 : 160), the former may be found in the writings of several of the 
pre-Linnaean botanists. The foundation of the idea of the formation, 
as understood by many recent writers, is the habitat; and from this 
point of view therefore it is fair to trace, as was done by Clements 
(1904: 12), the modern concept of the formation back to the old 
idea of the general habitat, even though the early systematists 
failed to realize fully the vital relations of habitat and vegetation. 
Linnaeus, in his Pliilosopliia Botanica (1751 : 263-270), distinguished 
twenty-five habitats, and mentioned their characteristic genera; 
whilst in the Stationes Plantanun (1754; 1760: 64-87) the 
characteristic species were enumerated. Many of these habitats and 
accompanying lists of species might easily pass muster as a 
summary of the corresponding modern plant formations; and one 
is therefore tempted to speculate as to what would have been the 
relationships of the branches of modern botany had Linneaeus 
developed this concept on the vegetational rather than on the 
floristic side. As it is, whilst the general habitat of the early 
systematists has become the formation of the plant geographer, it 
has long been the species-station of the taxonomist. 
Even earlier than Linnaeus, Tournefort (1717, iii.: 178, et. seq .) 
had more than an inkling of ecology when he distinguished the 
