SCIENCE AND INDUSTRY. 
The Migration and Dispersal of Weare 
By ELLINOR ARCHER, M.Sc. 
A weed may be defined as a plant which is growing where some othe; 
plant would be of greater economic importance, or where it is desired _ 
that no plants should be grown at all. It follows from this definition 
that a plant may be a weed in some places and not in others. To take, 
for example, the true Couch Grass (Agropyrun repens), which is a 
plant with a slight fodder value, and one which will grow in practically 
any soil. When it is in poor soil which would not support more 
nutritious fodder it may be considered as a useful plant, but when it 
is growing on soil which could support some such grass as Cocksfoot 
‘(Dactylis glomerata) it is a weed, and when it spreads into cultivated 
land or gardens it is a very troublesome weed, which is particularly 
difficult to eradicate owing to its hard, quick-growing, underground 
stems or runners, which are rather difficult to destroy. Another | 
example is the Foxglove (Digitalis purpurea), usually a garden plant, 
but it increases rather rapidly, and sometimes spreads into neighbouring 
fields, where it at once becomes a noxious weed, because it contains 4 
sufficient percentage of digitalin to be very injurious to stock. The 
digitalin which it contains also makes it of some value as a medicinal 
plant. Many plants are weeds under any circumstances, having neither 
fodder, ornamental, nor economic value, and it is interesting to realize 
how universally many of these plants are spread over the civilized 
world. In North America, the Indians knew the smaller Rib Grass 
(Plantago lanceolata) by the name of “ White Man’s Foot,’ because 
if seemed to spring up wherever the white man had passed. Since 
weeds follow ‘civilization, it is obvious that the spread of weeds, or 
more especially the migration of weeds, from one country to another, 
is caused by man, sometimes consciously, but generally accidentally. 
Tue Mierarion or Weeps. 
There are a few outstanding cases in Australia in which weeds 
have been deliberately imported from other countries by some misguided 
person either for sentimental reasons or because the plant has some 
little value for ornamental purposes. In the old days pioneers were 
anxious to make their Colonial settlements as much like their original 
homes as possible, and it seems most likely that for some such reason 
the popular but troublesome Scotch thistle (Onopordon acanthium), 
with its pretty purple flowers, but useless spiky foliage, was first brought 
to this country. 
There have been a good many cases of plants introduced for their 
ornamental value spreading to such an extent that they have caused a 
considerable loss of money. Perhaps the most notable example of this 
is the Water Hyacinth (Hichornia speciosa) ; this is a plant with a long 
racemes of pale lavender flowers, which are very attractive. The plant 
is a native of Guiana, South America, and has been introduced, with 
disastrous results, into a number of countries for the beauty of its 
flowers. In warm climates it is noted for the extraordinary rapidity 
of its growth and the quickness with which it spreads. In some of the 
rivers of-Queensfarid- and northern New South Wales it grows in such 
profusion that it blocks the whole river and interferes with traffic. 
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