102 Stapledon. — On the Plant Communities of Farm Land. 
from the field to be investigated, taken to the laboratory, the species 
separated out, and the number of plants belonging to each species is then 
counted and the results given as a direct percentage. 
Specific frequencies have been taken on over 75 fields and several 
hundred have been examined altogether. 
When frequencies or percentage figures are not available the species 
have been classified according to the following grouping, which experience 
suggests corresponds to the frequencies given against each : 
Dominant, e.g. 
Abundant, ,, 
Frequent, „ 
Occasional, „ 
Scarce or Solitary, „ 
Rare, „ 
frequencies 7-9 (10 is very exceptional) 
» 3~ 6 
„ 1-2 
„ less than 1 and as before 
>) )) >) }> 
33 3 ) 33 33 
Treatment of the Subject. It will be convenient to deal with the 
subject-matter under two distinct heads. Part I. The Weeds of Arable 
Land\ that is to say, the communities found under root crops, cereals, 
and ‘ seeds \ By { seeds J is here understood leys which are sown down with 
a mixture of grass and clover seeds for one year only, or if sown for a longer 
period, till the end of the first year. The above communities are under the 
direct control of man, and owing to the exigencies of the rotation are short- 
lived and consequently do not afford materialf or the study of the progressive 
stages in the colonization of bare land. Part II. The Weeds of Grass-land. 
This includes the communities found on long duration leys and on permanent 
grass, and affords material for the study of the progressive changes which 
occur in the colonization of land under the constant influence of grazing 
animals. For the sake of comparison two cases will also be given of the 
colonization of bare land from which stock have been withheld. 
PART I. 
The Weeds of Arable Land. 
Under this heading it is proposed to make the following comparisons: 
I. The aggregate arable flora of the Cotswolds with that of Mid- Wales. 
II. The results from Mid- Wales and the Cotswolds with those obtained 
elsewhere. 
III. The arable flora of Mid-Wales above and below 800 feet. 
IV. The weed flora under the several crops in the rotation. 
In order to facilitate these comparisons the frequencies found for a large 
number of species in both localities and in various places in the rotation are 
set out in the subjoined table (Table I). 
