1903] VEGETATION OF THE BAY OF FUNDY MARSHES 433 
low marsh great areas, to the exclusion of the dominant members, 
in such places becoming itself the dominant form. One cannot, 
however, trace all of the transitions to physical causes, and in 
places it seems as if we were dealing here with another case of 
unstable equilibrium, the forms acting in mass against one 
another. The same phenomenon appears in the bulls-eye 
daisy, groups of which appear amongst the dominant members 
in an apparently very irregular way, again suggesting that it is 
not physical causes alone which are responsible for their distri- 
bution, but that it is either the result of a struggle between nearly 
equally-matched masses of forms, or else that there is a large 
measure of pure accident in the details of their distribution rela- 
tively to one another. But of this we can know nothing until 
‘we learn how the forms “ compete” with one another. 
This association shows one very characteristic feature of an 
association, lacking in those heretofore considered, namely, a 
distribution of the aerial parts of its members in horizontal 
Strata. Forming the uppermost layer in the full blaze of the 
sun come the two dominant grasses. Nestling below the shade 
of their leaves, come the clovers and the Lathyrus, while in a 
third layer nearer the ground are the leaves of the violets, straw- 
berries, and other low forms which I have not tried ‘to list, 
all of which, of course, blossom in the early spring before the 
Stasses have grown tall. Here again we are faced by the ques- 
tion as to the real ecological interrelationships of these various 
forms, whether we have to do (1) purely with a mixture of forms, 
some of which happen to be able to live in the interstices left 
in the growth of other forms, or (2) whether the smaller derive 
some benefit from the shade or other protection of the taller, or 
(3) whether there may be some advantage to all the members 
from the association, such as we can imagine the taller timothy 
derives from the smaller but nitrogen-fixing clover. On these 
matters we still have no knowledge. 
As above stated, the marginal member of the association 
towards the Staticetum is the couch, and the marginal member 
towards the Macrospartinetum is the brown top, while that 
towards the Cnicetum is the bulls-eye daisy. 
