SUCCESSION. 23 
A climax formation is evidently in large part governed by climate 
(climatic), while a migratory formation in large part depends upon 
the nature of the soil, though, of course, in both formations soil and 
climate must count. Each of the plant-associations which taken 
together make up a migratory formation may be comparatively 
young, but the migratory formation as a whole must have existed 
longer upon the earth than the climatic formation of which it was 
and is a topographical phase. 
Each formation has, indeed, its life-history, which consists, after 
its beginning, in a series of changes, one transitory association 
giving place to another, and so on, until the final apparent stability 
comes. This interesting phenomenon is known as _ succession. 
Succession is of two quite distinct kinds, but only one of these 
is true biological succession. This is where the plants themselves 
during their competition lead to changes in the association apart 
from any topographic change, as when the open association of stony 
river-bed is finally transformed into tussock-grassland (fig. 13), or 
the debris-field of the high mountains into that plant-formation 
described in Chapter VI under the name “ fell-field”’ (figs. 69, 71). 
In the case of topographical change there is often no gradual 
progress, but rather the wiping-out of a complete association and the 
beginning again—.e., there is a series of migratory formations leading 
up to a climax association. The early association of rock-faces in a 
gully has but little to do with the final vegetation of the valley-floor. 
Succession of this kind may be called topographical succession. 
With regard to succession, the struggle for existence between the 
plants is a matter of prime importance. Such a strife is somewhat 
analogous to that which takes place, even in civilized human com- 
munities, between the individuals of the State, each of whom is 
either aided or burdened by characters, good or evil, handed down 
to him from his more or less remote ancestors. Thus under the 
environment created by civilization some become rich or famous, 
while others remain poor or may even become degraded. This 
latter misfortune could in no small measure be remedied were the 
teachings of biology not ignored and a more suitable environment 
provided. But it must not be forgotten that too much interference 
with the laws of nature must spell disaster. 
Every one who cultivates a garden, however small, has to cope 
with what are called “weeds ’”’—+.e., with plants not wanted which 
