THE  TROPICAL  AGRICULTURIST. 
[Oct.  I,  1896. 
258 
exorcised  the  minds  of  the  plant  physiologist  and 
agricultural  chemist. 
It  is  only  a few  months  ago  since  an  announcement 
was  made  to  the  German  Agricultural  Society  that 
certain  highly  interesting  experiments  carried  out  by 
Professor  Nobbe,  of  Tharand,  in  Saxony,  a well-known 
and  distinguished  authority  on  plant  physiology,  had 
culminated  in  the  production,  on  a commercial  scale,  of 
cultures  of  bacteria  for  use  in  agriculture;  and  that 
arrangements  had  been  made  with  one  of  the  largest  che- 
mical manufactories  in  Germany — the  very  same, indeed, 
which  has  already  undertaken  to  supply  the  medical 
world  with  the  antitoxic  serum  for  use  in 
the  treatment  of  diphtheritic  cases — to  supply 
these  cultures  to  any  who  might  disire  to  use 
them.  To  these  cultures  the  title  nitragin  has 
been  given ; and  at  the  present  moment  many 
experimental  trials  are  being  either  arranged  for,  or 
are  in  process  of  being  carried  out,  with  a view 
to  test  its  efficacy.  With  the  object  of  explaining  for 
our  readers’  benefit  the  significance  of  this  new  de- 
velopment in  agricultural  science,  a short  account  of 
the  experiments  which  have  led  up  to  it  may  be 
given. 
It  is  now  a number  of  years  ago  since  Pasteur  showed 
that  the  process  of  the  decay  or  putrefaction  of  or- 
ganic matter,  constantly  going  on  on  the  earth’s  sur- 
face, was  due  to  the  action  of  miro-organic  life. 
Subsequent  research  has  demonstrated  that  the  soil 
of  our  fields  is  literally  teeming  with  bacteria,  which, 
according  to  some  recent  experiments,  may  be  pre- 
sent to  the  extent  of  forty-five  millions  per  gramme 
(the  l-28th  part  of  an  ounce)  of  soil  ; and  that 
these  bacteria  are  largely  instrumental  in  con- 
ducing to  the  successful  growth  of  vegetation,  by  pre- 
paring, in  forms  suitable  for  assimilation  by  the  plant, 
the  different  food  substances  it  derives  from  the  soil. 
Most  of  these  substances  are  required  in  vegetable 
life  in  a simpler  form  than  that  in  which  they  are 
originally  present  in  the  soil ; and  it  is  in  converting 
these  more  or  less  complex  forms  of  food  material 
into  simpler  ones,  that  the  useful  role  of  the  soil- 
microbes  consists.  With  regard  to  the  nature  of  this 
minute  life  we  have  but  scant  knowledge ; but  we 
have  lately  become  acquainted  with  some  bac- 
teria which  are  concerned  in  the  preparation  of  that 
higfcly  valuable  plant  food,  nitrogen,*  in  forms  suit- 
able for  assimilation  by  the  plant.  It  has  long  been 
known  that  the  plant  absorbs  most  of  its  nitrogen 
in  the  form  of  nitric  acid,  or,  more  correctly  speak- 
ing, as  nitrates.  It  has  also  been  long  well  known 
that  nitrogen,  in  the  form  of  organic  compounds  and 
ammonia,  was  liable,  under  certain  conditions,  to 
be  converted  into  nitrates  in  the  soil  ; and  this 
knowledge  was  put  to  a practical  application, 
in  the  manufacture  of  saltpetre,  in  the  earlier 
days.  In  the  year  1877,  however,  it  was  discovered 
that  this  process,  to  which  the  name  nitrification  was 
given,  was  caused  by  the  action  of  micro-organic  life. 
Since' the  year  mentioned,  further  research  has  revealed 
that  at  least  two  separate  forms  of  bacteria  are  impli- 
cated in  this  process.  The  result  of  these  interesting 
investigations  has  been  to  show  that  the  fertility  of  a 
soil  depends,  to  a very  large  extent,  on  whether  or  not 
it  is  properly  stocked  with  the  nitrification  bacteria. 
But  a still  more  interesting  discovery  wdfs  made  in  the 
year  1886,  by  the  late  Professor  Hellriegel  and  Dr. 
Wilfarth  of  a class  of  bacteria  which  infest  certain 
nodulos,  'or  fleshy  excrescences,  to  be  found  on  the 
roots  of  leguminous  plants,  and  which  are  able  to 
render  the  free  nitrogen  of  the  air  available  to  the 
^^For  many  years  the  question, — can  plants  utilise 
the  free  nitrogen  in  the  air  ? — was  a keenly  debated 
one.  The  discussion  of  this  question  dates  from  the 
beginning  of  the  present  century.  Elaborate  experi- 
ments by  French  and  English  chemists  were  supposed 
* Nitrogen,  it  may  be  mentioned,  for  the  benefit  of 
those  unacquainted  with  the  science  of  plant-physiology, 
is  for  many  reasons  one  of  the  most  important  of  all 
nlants-foods.  It  may  be  described  as  the  regulating 
factor  of  plant  growth  ; and  tlio  question  of  its  supply, 
^n  forms  suitable  for  assimilation  by  the  plants  is,  for 
the  fanner,  of  the  highest  economic  importance. 
fo  have  decided  it  a number  of  years  ago:  and  it 
was  believed,  till  the  startling  discovery  already  re- 
ferred to  was  made,  that  plants  were  unable  to 
utilise  the  nitrogen  in  the  air.  In  justice  to  the  dis- 
tinguished experimenters*  whose  experiments  seem 
ill  contradiction  to  the  facts  of  the  case  as  we  now 
know  them,  it  may  be  explained  that  their  experi- 
ments were  carried  out  under  conditions  which  ex- 
cluded the  agency  of  bacterial  life.  It  should  also 
be  added  that  the  power  of  utilising  the  free  nitro- 
gen of  the  air  only  belongs  to  certain  plants,  such  as 
clover,  peas,  beans,  &c. — these  generally  grouped 
under  the  term  of  “ leguminous  crojps.”  This  inter- 
esting discovery  serves  to  throw  light  on  the  power 
possessed  by  certain  crops  of  resuscitating  soils 
on  which  other  crops  had  been  grown,  and  which 
had  thus  become  impoverished.  Even  at  so  remote 
a period  as  the  time  of  the  Komans  this  fact  had 
been  observed  ; and  the  adoption  ol  the  practice  of 
the  rotation  of  crops,  a very  old  custom,  may  be 
said  to  be  based,  to  a certain  extent,  on  the  re- 
cognition of  the  same  principle.  The  existence  of 
nodules  on  the  roots  of  leguminous  plants  was  a 
fact  which  had  also  been  long  known;  although 
their  true  function  had  been  for  long  little  suspected. 
The  details  of  the  process  of  nitrogen-fixation,  as 
it  is  called,  are  not  as  yet  known  with  any  accuracy. 
That  the  organisms  found  in  these  nodules  invade 
the  roots  from  the  soil  and  thus  give  rise  to  the 
formation  of  the  nodules,  seems  to  be  clearly  proved. 
There  they  multiply  with  great  rapidity  and  stimulate 
thegrowth  of  the  plant-cell.  Liviugat  firstat  theexpeuse 
of  the  plant,  as  parasites,  thej'  gradually  become  pas- 
sive and  the  cells  then  become  filled  jWith  bacteroids 
or  bacterium-like  bodies.  It  is  when  this  period  is 
reached  that  the  plant  absorbs  the  contents  of  the  no- 
dules, and  leaves  the  cells,  out  of  which  they  are 
formed,  in  a limp  condition.  It  seems  doubtful 
whether  there  are  several  kinds  of  fixing  bacteria,  or 
whether  the  organism  becomes  so  altered  in  itsgrow'th 
with  the  plant  that  it  is  not  suited  for  promoting 
the  growth  of  other  leguminous  plants.  Whatever 
the  explanation  may  be,  it  has  been  found  that  the 
organisms  suitable  for  affecting  the  fixation  of  nitro- 
gen for  certain  plants  are  not  able  to  act  in  the 
same  capacity  for  other  plants. 
We  need  not  enumerate  the  experiments  carried 
out  to  test  the  accuracy  of  the  above  theory. 
Those  interested  in  the  question  we  would  refer  to 
two  interesting  papers  on  the  subject,  in  the  lately 
issued  Journal  of  the  Iloyal  Agricultural  Society  of 
England,  by  Dr.  Miller  and  Dr.  Voelcker.  The  early 
experiments  on  a practical  scale  were  made  by  inocu- 
lating soils,  ou  which  leguminous  crops  h.ad  been 
found  by  practice  not  to  do  v/ell,  with  soil  from  fields 
containing  tho  nitrogen-fixing  bacteria  in  large 
numbers.  To  effect  this  satisfactorily  it  was  found 
that  110  loss  a quantity  than  16  cwt.  of  soil  had  to 
bo  used  per  acre.  'This  method,  besides  proving 
cumbersome,  is  not  free  from  other  objections,  since 
organisms  other  than  the  nitrogen-fixing  ones — orga- 
nisms which  may  exert  a distinctly  unfavourable 
action  on  plant  growth,  as  well  as  induce  fungoid 
diseases  of  parasitic  growths — may  be  present  in  the 
soil  thus  applied.  Professor  Nobbe  consequently  set 
himself  to  obtain  pure  cultures  of  the  fixing  bacteria  by 
the  usual  bacteriological  methods.  Inasmuch  as  the 
different  leguminous  crops  require,  as  we  have  already 
explained,  either  separate  organisms  or  else  different 
modifications  of  the  same  organism.  Professor  Nobbe 
has  prepared  a large  number  of  pure  cultivations  suited 
for  the  commoner  leguminous  crops  grown.  These 
cultures  are  preserved  in  glass  bottles  containing 
ayra-fjclalinc — a commonly  used  developing  medium 
— and  arc  of  eight  to  ten  ounces’  capacity.  They 
have  to  bo  kejit  from  tho  inlinenco  of  the  light, 
and  care  must  be  taken  not  to  expose  them  to  a 
temperature  above  <.»8  deg.  Fahr.  Inoculation  of  a 
soil  with  these  cultures,  on  a practical  scale,  may 
be  effected  in  cither  of  two  ways.  First,  the  seed 
of  the  crop  it  is  desired  to  inoculate  may  be  inocu- 
* 'The  experimenters  referred  to  arc  M.  Boussiu- 
gault.  Sir  J.  B.  Lawos  {of  Kothamstod)  Sir  J.  Henry 
Gilbert,  and  Dr.  Pugh, 
