64 Effect of Arsenic Compounds 



niger, larger doses up to 1/8 % retard growth, while 1/6 % kills. Spores 

 of the fungus taken from soil containing arsenic are said to possess an 

 immunity against arsenic, in that they germinate in the presence of an 

 arsenic content which rapidly kills control fungi. This immunity is not 

 specific for arsenic, but extends also to other poisons. The chemical 

 composition and water content are not altered. 



Conclusion 



The toxic effect of arsenic upon higher plants is much more marked 

 with arsenious acid and its compounds than with arsenic acid and its 

 derivatives. No definite evidence of stimulation has yet been obtained 

 with any arsenic compound, however great the dilution at which it is 

 applied. With certain algae a stimulus may occur, and it is possible 

 that arsenic acid is capable of replacing phosphoric acid to some extent 

 under certain conditions. With fungi the toxic effect of great con- 

 centrations is marked with certain species, but there are others which 

 are capable of living happily on arsenical compounds and of liberating 

 highly poisonous arsenic gas. 



