212 NOTES ON ALIEN AND CASUAL PLANTS.
with 46 per cent. each, Ranunculaceae with 44 per cent., Um-
bellifera 41 per cent., Chenopodiaceae with 40 per cent., Scrophu-
lariaceae with 36 per cent, Caryophyllacea 35 per cent.,
Rosacea 19 per cent., and the Cyperaceae with one out of 105
species, which is less than one per cent. It is easy to understand
why the Leguminosae and Crucifera should be so well repre-
sented, so many of them being of economic value, or associated
with crops, but one would scarcely have expected the Boragi-
nacea to rank so highly. On the other hand one would have
thought that the grasses as fodder crops and Asteracea with
their flying seeds would have shown a greater percentage of
foreign introductions. The records for Essex do not work out
to anything like the same proportions, probably because they
are, at present, by no means complete.
When a piece of land is cleared and cut up for build-
ing purposes, the removal of turf, digging of foundations,
excavations for sewers, and other processes, necessarily
cause a great disturbance of the surface soil, and what is not
immediately built on forms a fine nursery for the straying
seeds of innumerable plants, which readily germinate and grow
in bare soil without much regard to its composition and texture.
Were the operations to stop here the ground would soon be
covered with a selection of the most enterprising species already
established in the neighbourhood, with, perhaps, a few whose
seeds had lain for years dormant in the soil, awaiting such a
disturbance to enable them to germinate. But in addition to
these preparatory stirrings there is imported into the district
a quantity of shingle, gravel, ballast and other material for the
make-up of the roads and other purposes, and since this will
probably come partly from other districts and partly from other
countries, numerous plants strange to the neighbourhood are
almost certain to spring up. From these considerations it is
scarcely necessary to say that building estates are on the whole
the most fruitful areas in alien and casual plants, but land
which has been laid waste in any way will generally
repay the seeker after such strays.
I will now proceed to what most of you no doubt will consider
the more interesting part of my paper and give the results of
my own explorations in Hale End and Woodford, where much
spasmodic building goes on.