20 
C. E. Moss. 
and with regard to the grouping of allied associations into formations, 
the opinion can he fully justified. 
Perhaps too much stress has been laid by critics on the 
particular terms employed by plant geographers, and too little on the 
concepts which the terms were intended to convey; and the object 
of the present communication is to endeavour to trace the historical 
development of the harmonious elements now existing in the 
concepts relating to plant associations and formations, and to give 
to these general ideas those terms which historical and present day 
usage would seem to indicate as right and proper. 
It must be remembered that, in the development of every 
branch of knowledge, a time occasionally arrives when it becomes 
necessary to expand a concept which for long has been attached to 
a particular term. A few years ago, for example, it was held to be 
desirable to extend the signification of the term seed so that it 
should be applicable to integumented megasporangia destitute of 
embryos. So long as the expansion of a concept is due to a real 
advance in knowledge, and so long as the broader conception is in 
harmony with the more fundamental aspects of the previous use of 
the term, the new use is not merely legitimate and desirable but 
absolutely essential, unless all branches of learning are to be 
overburdened with new terms whenever concepts undergo a 
necessary, logical, and developmental expansion. 
The Plant Association. 
The concept of the plant association is one of the oldest in plant 
geography. Without referring to the literature of the ancients, in 
which doubtless the germs of these concepts may be found, it is 
sufficient to say that, with regard to the plant association, the 
concept and the term were used by the illustrious Humboldt more 
than a century ago; whilst the term formation dates from the time 
of Grisebach (1838). Humboldt showed that he had a well-defined 
concept of the plant association even when he did not use the term, 
as the following passages illustrate (Humboldt, ?1806 ; Sabine’s 
English tr., 1849: 264):—“In the temperate zone, and especially 
in Europe and northern Asia, forests may be named from particular 
genera or species, which, growing together as social plants, form 
separate and distinct woods. In the northern forests of oaks, pines, 
and birches, and in the eastern forests of limes or linden-trees 
usually only one species of Amentaceae, Coniferce, or Tiliaceze 
