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 avicenniae, 

 which is from British India. 



As a rule, 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 (Rmnex acetosella). 



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