44 COMMON WEEDS 



Docks, and other strong-rooted plants left in the ground 

 ammonium sulphate tends to destroy them. (See also 

 p. 346.) 



2. Common Salt is a deliquescent substance which 

 extracts water from damp air and surrounding objects 

 with which it may be brought into contact. When 

 applied to succulent plant tissues it draws water from 

 them and produces an effect similar to drying or 

 scorching ; leaves to which it is applied are killed, 

 and look as if they had been burnt. Salt may be used 

 on a small scale for the destruction of Nettles and 

 other weeds, and its application has been found bene- 

 ficial in checking weeds and indirectly improving the 

 useful herbage of grass land. The semi-parasites 

 Yellow Rattle (Rhinanthus) and Louse wort (Pedicularis) 

 are reduced by it. 



3. Carbolic Acid, I pint thoroughly mixed with 

 4 pints of water, has been found a very efficient 

 weed killer. It is most frequently used on small areas, 

 at the rate of 8 gallons per square rod. It was found 

 at the Woburn Experiment Station of the Royal Agri- 

 cultural Society that Wild Onion (Allium vineale) may 

 be destroyed by carbolic acid (see pp. 126, 209). 



4. Sodium Arsenite. This substance, or allied com- 

 pounds of arsenic, is the basis of many of the pro- 

 prietary weed-killers sold by chemists and nurserymen. 

 It is one of the most effective of all plant poisons, 

 but cannot be used for weeds on cultivated ground or 

 on grain land, because it not only destroys weeds but 

 kills all other vegetation as well, and prevents crops 

 from being grown on that soil for a considerable time 

 afterwards. It may be properly used on paths, gravel 

 courts, and similar places where vegetation of all kinds 

 is out of place. Its highly poisonous and dangerous 

 character, however, precludes it from general use. 



