The  Production  of  Plant  Food  in  the  Soil. 
15 
Un 
treated 
soil 
Heated 
soil 
Un- 
treated 
soil 
Soil  treated  with— 
Carbon 
Disul- 
phide 
Toluol 
Chloro- 
form 
Oxygen  absorbed  . 
100 
215 
100 
151 
157 
118 
Weight  of  crop  pro- 
duced  . 
100 
153 
100 
128 
116 
138 
(Mus 
tard) 
(Bucl 
wheat) 
The  part  played  by  bacteria  was  very  evident  when  the 
crops  were  analysed  so  as  to  furnish  information  as  to  the 
quantities  of  plant  food  present  in  the  different  soils.  In  all 
cases  the  partially  sterilised  soils  contained  more  plant  food 
than  the  untreated  soil,  an  observation  fully  in  accordance 
with  the  observed  increases  in  bacterial  activity  ; the  results 
are  shown  in  diagram  form  in  Fig.  1.  All  these  results  point 
to  one  conclusion  ; when  a soil  has  been  partially  sterilised,. 
i.e.,  treated  so  that  the  active  forms  but  not  the  spores  of  the 
□ 
Soil  Untreated. 
1 
Soil  treated  with  Toluol. 
FlO.  1. — Relative  amounts  of  plant  food  taken  by  buckwheat  from  variously 
treated  soils. 
micro-organisms  are  killed,  then  the  new  population  arising 
from  the  spores  is  more  numerous  and  more  active  than  the 
old  one. 
This  conclusion  was  followed  up  by  Dr.  Hutchinson  and 
the  writer  in  an  investigation  of  the  changes  brought  about  by 
Soil  treated  with  Chloroform. 
Soil  treated  with  Carbon  disulphide. 
