Arable Land 
or Senecio viscosus luxuriating on the Glasgow rubbish 
heaps or “blaes.” Sea-side plants, such as Euphorbias, 
Chenopodiums, Silverweed, are very common as weeds. 
One of the very worst weeds in America is Salsola 
kali, which is a sea-side plant with us, but also occurs 
abundantly in the salt deserts of Central Asia. 
But weeds may come from anywhere; thus, for ex- 
ample, in an orange garden at Tripoli, in Africa, I found 
quantities of an American nettle (U. membranacea). 
Spain is full of South African and American weeds 
growing so vigorously that one would never suspect 
them to be foreigners, 
So also in the United States, one finds in cultivated 
ground the poppy (Papaver dubium), an European im- 
migrant which is travelling westward at the rate of five 
miles in three years, also the Mexican P, argemone from 
the tropics of Central America, and Abutilon avicenniz, 
which is from British India. 
As arule, weeds in their native lands belong to “ open” 
floras, that is, grow apart from one another and sparsely 
or scattered. Being hardy, stubborn, inured to dry 
ground, and able to grow rapidly whenever they have 
the chance of doing so, they may be of very great impor- 
tance in colonising the ground. 
An interesting case of good work performed by weeds 
is recorded from Wardale (Trondjhemfjord) by Resvoll. 
A serious landslip occurred there during 1893, and in 
consequence the valley was entirely plastered over by a 
surface of raw, unworked clay which covered it for a 
space of 8000 yards long and about a thousand wide. 
Five years afterwards it was green and fresh, with a 
fine and thick growth of plants, amongst which honour- 
able mention should be made of coltsfoot, knotgrass, 
(Polygonum aviculare), mouse-ear chickweed, and 
sheep’s sorrel (Rumex acetosella). 
255 
