WOODHAM WALTER COMMON 27
map with Fig. 3 shows that the bracken is dominant on the
sandy soils, sparse on the clay fringing the sand, and absent
from the clay in the valleys, while comparison with Fig. 4
Fig. 5. Distribution of Bracken.
shows that it is confined to the regions occupied by oak. The
growth of bracken is thus determined firstly by the nature of
the canopy : it cannot grow under hornbeam which casts too
dense a shade; but it can grow under oak which casts a less
dense shade. Secondly, the growth of bracken is influenced