NOTES ON ALIEN AND CASUAL PLANTS. 211
it was introduced. Mr. Shenstone's first question," What is a
casual?" I have already answered, and the others are easily
dealt with. All the plants that are positively known, or strongly
suspected, to have been introduced into an unnatural locality
by human agency may be classed as casuals, and once a casual,
always a casual, whether established or not. I need not enu-
merate the multitude of methods by which plants in general
are disseminated, but it will be necessary to mention some of the
ways in which alien and casual plants may be introduced. Of
these probably the most effective are : (1) the importation of
the seeds with all kinds of cereal and other farm seeds, which
are usually sifted before being used in this country and the
siftings thrown out, the numerous foreign seeds amongst these
germinating ; (2) the introduction of ballast from other countries,
which being dumped at our ports often remains long enough
fo allow seeds brought in with it to germinate, if the weather be
suitable ; (3) the carriage of this ballast to the various parts of
the country by rail and the consequent direct distribution of
the contained seeds. Minor causes of dispersal are : (4) the impor-
tation of wool, hides, and other merchandise to which adhesive
fruits and seeds of many kinds stick and are removed on their
arrival in this country ; (5) the considerable use of certain
foreign seeds for cage birds, the seeds being thrown out with the
sand when the cages are cleaned out and so perhaps become
established in gardens from which they may spread to surround-
ing waste land and so get distributed ; (6) the gardens, nurseries,
game coverts, and other places where exotic trees and plants
are cultivated, constitute sources of alien supply for the surround-
ing districts ; (7) the deposition of refuse outside towns by the
local authorities ; (8) the importation of hay and other forage
and plants for agricultural use, is another source of aliens, though
a small one.
In his List of British Plants, which comprises the Phanero-
gams and Pteridophyta, G. C. Druce includes about 1,100 aliens
and casuals, of which I have notes of nearly 200 for Essex. On
studying Druce's list I find that of the great Orders (i.e. those
containing 50 or more species) the Leguminosae rank highest
with 67 per cent. of aliens and casuals, the Boraginaceae next
with 64 per cent., and then the Cruciferae with 63 per cent.;
next the Graminaceae with 48 per cent., Lamiaceae and Asteraceae