1903} VEGETATION OF THE BAY OF FUNDY MARSHES 301 
upon degrees of the physical factors determining the formations, 
though in larger part upon a quite different principle, namely, the 
ecological interrelationships of the plants to one another, 
particularly with reference to the ability of different forms to 
occupy the same ground at the same time without serious inter- 
ference and perhaps with positive benefit to one another. Such 
groups are called appropriately associations, and they often are 
recognized and named locally by the prominent forms, such as 
oak-forest, broadleaf marsh, etc. Formations and associations 
are thus both distinct ideas and distinct groups, the former hav- 
ing the physical or physiographic idea prominent, and the latter 
the idea of ecological interrelationships of the plants, involving 
their competition and cooperation. Of course the two merge 
into each other, and often coincide, and by many students they 
are treated as one. Their delimitation, while often easy, is some- 
times very difficult. As in all such cases they can be studied 
and described only by the selection of typical examples, all 
intermediate forms being described in terms of the typical. The 
associations are made up of the vegetation-forms, the ecological 
units, best treated for the present, as above explained, as 
coincident with species. These vegetation-forms constitute the 
members of the association, but of varying degrees of importance. 
Some are evidently far in the lead in size, numbers and importance 
— they are dominant ; others are close to these and struggling for 
the leadership —they are secondary; others are much less con- 
Spicuous, but manage to maintain a position among the preceding 
in spots not occupied by them—they are subordinate. Then in 
addition to the members may be recognized the frequent visitors 
from neighboring associations, and various strangers or strag- 
glers from more distant positions. But a satisfactory terminol- 
ogy of the degrees of membership must await an understanding 
of the real nature of their interrelationship, a knowledge which 
we do not yet possess.%5 
35 The distinction here drawn between formations and associations will not be 
admitted as valid by all, at least to the degree here held, but I believe it represents a 
real fact in nature and will stand. There is moreover an increasing tendency to 
recognize the distinction as well as to use this terminology. It is used by Kearney, 
y Lloyd and Tracy, and by Harshberger (though he calls the association a society). 
