Fundamental Units of Vegetation. 
19 
better with regard to the formation, association, and society ; for the 
units of the plant-geographer agree with those of the systematist in 
being entities which are not invariably sharply marked off Irom 
each other in nature. Much, however, of the prevailing confusion 
in phytogeographical nomenclature lies less deeply seated than this; 
and to some extent, therefore, the malady is one of which hopes 
may be entertained of an ultimate, if not of a speedy cure. 
The need of greater harmony in the use of terms in ecological 
plant geography was recognized at the International Congress of 
Geographers held at Berlin in 1899, and by the International 
Congresses of Botanists held at Paris in 1900 and at Vienna in 
1905 ; and the matter is also to be considered at the forthcoming 
International Congress of Botanists to be held at Brussels in May, 
1910. Warburg (1900), Flahault (1900-1901), Clements (1902), 
Olsson-Seffer (1905), and Gradmann (1909) have published papers 
dealing specially with matters of phytogeographical nomenclature ; 
but their differing schemes and recommendations have not brought 
about the desired uniformity. 
Warburg’s suggestions were of a tentative and general nature, 
and referred to the nomenclature of groups of formations rather 
than to formations themselves. Flahault’s suggestions were two¬ 
fold, relating, on the one hand, to “geographical and topographical 
units,” such as regions and zones, and, on the other hand, to 
vegetational or “ biological units,” such as associations and 
formations. Clements’ suggestions received a severe handicap in 
meeting with the immediate disapproval of Engler. Whilst it 
must be confessed that Clements’ system was perhaps in some 
respects too elaborate to be workable, and that parts of it were 
undesirable on general grounds, it is to be feared that the prompt 
displeasure expressed by such an eminent plant geographer as Engler 
had the unfortunate and doubtless undesired effect of preventing 
certain other portions of Clements’ scheme from receiving a fair 
and unbiassed consideration. 
Recently, Warming (1909) has issued a book in English on the 
(Ecology of Plants ; and Professors Flahault and Schroter, in a 
leaflet circulated in connection with the forthcoming Congress at 
Brussels, have stated their opinion that this book solves nearly all 
the difficulties connected with phytogeographical nomenclature. It 
seems difficult, however, to support this opinion in the matter of 
Warming’s use of the term formation ; although, in certain other 
particulars, especially with regard to the use of the term association 
