452 BOTANICAL GAZETTE [DECEMBER 
another. Or we may express the situation thus. Ecological 
plant geography is the study of the actual adaptations of masses 
of plants as they grow together in nature. The physics of the 
environment, plus the physiological properties of the plant, tend 
to give as a resultant a certain general vegetation-form.; this, 
plus cooperation and competition, gives the actual groupings in 
a vegetation. 
That plants do in some way compete with one another, that upon 
the same ground some kinds can drive others out and take posses- 
sion, is, of: course, evident to observation. That, on the other 
hand, certain kinds of plants can combine and cooperate for the 
common good is, I think, equally true. In both cases we know 
some of the general causes which determine the results of both 
competition and cooperation, but as to the details we know 
nothing. Seven years ago Warming, in his great book, said: 
“There is scarcely a more attractive biological field than to 
determine what the weapons are with which plants force one 
another from their positions,’’ but today we know no more of 
that subject than when Warming wrote those words. Yet eco- 
logical plant geography cannot advance, nor can we understand 
the vegetation of a country or district, until we understand this 
subject, and we but blind ourselves and only imperfectly con- 
vince others by our present generalizations. The crucial point 
in competition is this: by what weapons or methods does one 
plant overcome another, when the result is determined between 
the plants and not by the environment. Ina broad way we can 
often see general reasons why one plant should dominate another ; 
the more rapid growth of one kind, or larger size, or the replace- 
ment of a shade-loving by a sun-loving kind, or the entrance of 
a new kind when one form has exhausted the needed minerals 
from a soil, etc., seem to give an ample explanation. But even 
in these cases, and especially in the many cases where the kinds 
seem evenly matched, we do not know precisely the method by 
which one kind manages to displace another. It is obviously 
by means of no visible carnal weapons such as animals use, nor 
is it a mechanical forcing aside of a weaker kind, for often there 
is ample standing room for the vanquished with the victor. 
