PLANT ASSOCIATIONS 227 
the ground was once or is still being periodically broken 
by the plough and sown with seed. Even the moorlands, 
where farmsteads are absent, have been interfered with 
for the rearing and preservation of game. But the 
greatest departure from the natural association is made 
in cultivated ground regularly ploughed and sown with 
crops. Here are found a number of agricultural weeds, 
mostly annuals and aliens, which, following in the track 
of civilization, have spread over all our arable fields and 
the waste places near, where the ground is frequently 
disturbed (see p. 215). 
Yet, in spite of all this interference by man, the depar- 
ture from the natural association is really not very great. 
The trees found growing in a plantation are trees which, 
after all, are suitable to the soil, and in many cases they 
would be found growing there naturally. The flowers of 
the field are wild, and the struggle for existence between 
plant and plant, and association and association, goes on 
much the same as if man did not interfere at all. Man 
only modifies or assists the conditions under which Nature 
acts ; he works and prepares the ground for the change 
from one association to another (as in draining a marsh 
or moor, or cutting down a wood), but the association 
that comes in is natural enough in all its main characters. 
The chief associations belonging to each type of vegeta- 
tion will be described later on, but, generally speaking, 
any association should be examined frequently during the 
year, and the following points recorded : 
1. The dominant plant or plants—z.e., the most 
common or the most conspicuous plants. 
2. The sub-dominant plants, which accompany the 
dominant forms, and, in a few places, supplant them. 
3. The other plants occurring in the association—noting 
whether they are social or scattered, abundant, frequent, 
local, rare, or casual. 
4. The succession of plants in flower throughout the 
year. 
» «5. The number of different species in flower at the same 
time. 
When two or more plants are dominant at the same 
time, or when one plant is dominant at one time of the 
year and others at a different time, the underground 
parts of the plants should be examined, for the roots 
