74 PROTECTION OF PLANTS, 1917-18 



one gallon of Sodium Arsenite solution. The spray was directed chiefly at the 

 thistles present. Other species occurring on the plot were white clover, dande- 

 lion, yarrow, tall buttercup, wild strawberry. On 10th July the thistles were 

 quite blackened. One-half of the plot was again sprayed all over with sodium 

 arsenite on 13th July; on 18th July it was observed that not only the thistles 

 but grasses and m,os^ other vegetation were killed down to the ground level. 



Destroying Weeds by Heat. 



Although this method scarcely comes under the title given at the head of the 

 present article, still, as it is so different from the usual methods of destroying 

 weeds, it may conveniently be referred to here. 



A burning machine which uses 8 gallons of petroleum per acre has recently 

 (1916) been tried in England. It consists of a number of blow-lamps like those 

 used by painters, which project a very hot flame on to the surface of the ground 

 thus destroying all weed growth. It has been used successfully to clear off the 

 weeds between currants and gooseberries planted in rows. 



A somewhat similar idea was last year (1917) put into practice on the 

 Spokane, Portland and Seattle Railway. A locomotive was provided with a series 

 of blowtorches. arranged a few inches above the rails. It proved quite efficient in 

 destroying weeds on the track. 



Weeds That May be Destroyed By Chemical Methods. 



For land that does not bear any crop, taking the question of cost into con- 

 sideration, the most useful substances will probably be common salt, arsenite of 

 soda, and fuel oil. In the case of shrubby growths if they are sprayed with 

 fuel oil and then sprayed again when the leaves are dry and dead they may 

 easily be set on fire. 



A South American railway company uses the following mixture to keep the 

 track free from weeds; — white arsenic 72 grams, caustic soda 15.5 grams, 

 phenolphthalein sufficient to give an intense coloration, water to make up to 100 

 cubic centimetres. One part of this solution is added to 10 of water and applied 

 by a special apparatus at the end of a freight train at. the rate of one quart per 

 square yard. The Columbia and Ecuador Railways have adopted a liquid com- 

 posed of equal volumes of a 17% solution of nitrate of soda and a 20% solution of 

 arsenious acid. 



Ferns. — On hilly pasture lands the most troublesome ferns are the Hay- 

 scented Fern {Dennstaedtia ptmctilohula Moore) and the Brake or Bracken 



