Fundamental Units of Vegetation. 21 
prevails or is predominant.” After thus referring to pure associations, 
Humboldt continues with reference to mixed associations: —“Tropical 
forests, on the other hand, decked with thousands of flowers, are 
strangers to such uniformity of association. A countless number 
of families are here crowded together; and, even in small spaces, 
individuals of the same species are rarely associated.” “The existence 
of a heath,” according to another passage from Humboldt (1819: 
295), “ always supposes an association of plants of the family of 
ericce .” It is perhaps scarcely to be expected that the originators 
of great conceptions should always have kept them within consistent 
and logical bounds, especially when these conceptions were closely 
related to wider but, at the time, unformulated ideas; and it is not 
surprising, therefore, that Humboldt should occasionally comprise 
groups of associations within his term association. Thus it was, 
perhaps, when he wrote as follows (1807: 17):—“ Les bruyeres, 
cette association de Yerica [Cal tuna ] vulgaris, de Y erica tetralix, des 
lichen icmadophila et hcematomma se repandent depuis l’extremite la 
plus septentrionale du Jutland, par le Holstein et le Luneberg, 
jusqu’au 52 e degre de latitude.” In the same essay, Humboldt 
(1807: 15), after mentioning such plants as Vaccinium Myrtillus, 
wrote :—“ Ces plantes associees sont plus communes dans les zones 
temperees que sous les tropiques, dont la vegetation moins uniforme 
est par cela meme plus pittoresque.” The modern concept of the 
plant association as well as the term may thus be traced to the works 
of Humboldt; and this concept and this term have, after many 
vicissitudes, come into very general use in the writings of modern 
ecologists and plant geographers. 
Schouw(1822; German tr., 1823: 165) briefly mentioned a 
few plant associations, and invented a method of denoting them. 
To the stem of the generic name of the dominant plant of a pure 
association, he applied the suffix -etum. Thus a plant association 
whose chief constituent is the beech ( Fagus sylvatica ) he termed a 
Fagetum. Similarly Schouw referred to Palmeta, Pineta, Querceta, 
etc. Meyen (1836; English tr., 1846: 78, 80) spoke of Ericeta t 
Fageta, Oliveta (sic), Palmeta, and Pineta. This matter is important 
in more than its nomenclatorial aspect, a matter which is discussed 
later on in this paper, for it proves that the concept of the 
association, had become firmly established in the minds of plant 
geographers of different nationalities before Grisebach had enunciated 
his famous definition of the formation. 
This definition was put forward in 1838 ; and, although 
