8
the latter often in their hundreds, Blue
Fleabane, Yellow-wort, Centuary, and some-
times Pyramidal Orchid and Greater Knapweed,
- closely followed by Knapweed, Birdsfoot-
trefoil, Grass Vetchling, Cowslip and Sulphur
Clover. Eventually the Pyramidal Orchid,
Yellow-wort and Greater Knapweed succumb to
competition, followed in time by the Bee
Orchid, Blue Fleabane and Centuary. On
some well-drained verges, where erosion
maintains a more open sward, with patches
of bare soil, the Bee Orchid and Centuary
persist indefinitely, just as they do on
the chalk.
The main indicator species of the type (ii)
verge, however, is the Sulphur Clover.
Like most other clovers it spreads mainly
by seed, but nowadays it seldom gets the
chance to flower, let alone seed, before
the flail mower crops it. Over the years
it has vanished from many miles of verge as
the annual mulch from the flail mower enriches
the soil and encourages competition from
ubiquitous rank weedy species. On the drier
verges, paradoxically, it actually seems
to benefit from flailing, the mowings
drying rapidly and dispersing, and flailing
gives it an in situ advantage - unfortunately,
however, it cannot seed and colonise new
verges .
(iii) The third type of boulder clay verge
occurs on the fragmented ridges between
the valleys of our major south-east flowing
rivers. Here the boulder clay is extensively
weathered and leached of most of its chalk
in the surface layers. It is characterised
by being unable to support the Sulphur Clover.
Otherwise its flora is not particularly re-
markable and resembles that of the London