The  Production  of  Plant  Food  in  the  Soil.  25 
and  thus  leaves  the  bacteria  free  for  a time  to  multiply  and 
to  make  plant  food. 
Turning  now  to  the  effect  of  volatile  antiseptics  on  the 
soils,  the  phenomena  observed  by  practical  men  can  be 
accounted  for  without  difficulty.  As  already  mentioned,  vine 
growers  have  for  over  fifty  years  injected  carbon  disulphide 
a b c 
FIG.  7.— Wheat  growing  on  poor  soil  without  manure,  a.  soil  heated  to  212°  F.  ; b, 
untreated  soil ; c,  soil  treated  with  toluol.  (Russell  and  Hutchinson,  Journal  of 
Agricultural  Science,  1909.  Vol.  3,  page  111.) 
into  their  soils  to  kill  phylloxera.  So  successful  was  the 
treatment  that  it  became  very  widespread  ; it  is  recorded  that 
in  1873  over  200,000  acres  were  receiving  carbon  disulphide. 
The  introduction  of  American  stocks  for  grafting  got  over 
the  difficulty  in  a cheaper  manner,  and  the  practice  has 
steadily  declined  ; it  is,  however,  still  followed  to  some  extent 
