SCIENCE AND INDUSTRY. 
Sand and earth used as ballast in an empty ship, and dumped in a 
convenient spot at the ship’s destination, carries with it its original 
flora. As it has usually been taken from some waste spot, this flora 
will be a fine crop of useless and noxious weeds. Any of these that 
have survived the voyage are being given an excellent opportunity to 
make a way for themselves in a new country. 
The migration from farm to farm and from district to district is 
frequently affected by unclean agricultural instruments.. The plough 
or harvester will pick up bulbs, stems, and seeds in an infected district 
and carry them to clean parts. 
The migration of weeds may be carried on to a certain extent by 
causes which, as a general rule, lead to their dispersal over a more 
limited area. Birds exert a great influence on dispersal, many seeds 
having developed special devices enabling them to cling to feathers, 
beaks, and claws. Migratory birds may carry a few isolated seeds over 
considerable distances, but the amount of harm done by the carrying 
of weed seeds in this manner is very slight. Many seeds cling to the’ 
wool and fur of animals, and this has led to the establishment of a 
small colony of 46 typically Australian plants on the banks of the 
River Tweed, in Scotland, the seeds of which have been deposited there 
by the scouring of Australian wool in the river. It is a popular 
fallacy that the seeds of thistles, and other plants with special adapta- 
tions for catching in the wind, can be blown immense distances.» As 
a matter of fact, the seed itself is seldom carried very far, it is only the 
disarticulated pappus which will be found floating in the air some 
miles from any plant of the same species. As a general rule, seeds are 
only carried across oceans, and from country to country, by man himself. 
It often happens that noxious weeds are not introduced directly from 
the country to which they are native, but come in a roundabout way 
from other countries in which they have previously been established. 
The Cape Weed (Cryptostemma calendulacea), a weed which is widely 
spread through our meadows and pastures, is a native of Africa, but 
reached -Victoria from Western Australia; whereas dodder, a native of 
Europe, was introduced into Australia by impure seed from New - 
Zealand. ; 
Tur DispersaL or WEEDS. 
The dispersal of a weed in a district into which it has once been 
introduced is a matter practically dependent upon the plant itself and 
upon the adaptations it has developed to insure dispersal. In order to 
become a troublesome weed, a plant will have developed along a line 
which in some way enables it to spread more rapidly than the surround- 
ing plants, to withstand unfavorable circumstances, to be unpalatable 
to browsing stock, or in some way have an advantage over its 
neighbours. To take, for example, the common little Chickweed 
(Stellaria media), this tiny, insignificant plant grows and ripens its 
seeds in six weeks. Each plant bears a good many flowers, and every 
flower produces numerous seeds. ‘This, together with the fact that the 
seeds can retain their vitality for several years, gives the plant every 
opportunity to spread rapidly and to keep its place in any district — 
where it has once appeared. Many plants, such as the Cow Thistle 
(Carduus orvensis), *St. John’s Wort (Hypericum perforatum), 
Bracken Fern (Pleris aquilina), and the Nettles (Urtica), have a 
strong development of underground thorizontal stems. These spread 
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