The  Woburn  Pot-Culture  Experiments , 1909.  345 
These  figures  show  that  a point  has  now  been  reached 
where  the  application  of  salts  of  lithium  ceases  to  be  injurious, 
but  would  even  appear  to  have  a stimulating  effect.  This  was 
most  marked  with  the  nitrate.  Simultaneously,  it  would  seem 
to  be  brought  out  that  caesium  salts,  in  the  quantity  here  used, 
exerted  no  injurious  influence  ; the  only  indication  of  this 
being,  possibly,  with  the  carbonate. 
Accordingly,  we  may  conclude  from  the  series  of  experi- 
ments with  lithium,  now  conducted  over  several  years,  that 
salts  of  this  metal,  supplying  it  in  not  greater  quantity  than 
•002  per  cent,  of  the  soil,  will  do  no  harm,  but  that,  when 
given  above  that  quantity,  they  will  have  an  injurious  effect 
on  the  wheat  plant.  Caesium  salts,  on  the  other  hand,  would, 
so  far,  appear  to  have  no  injurious  effect  even  when  used  in 
amount  to  give  '0036  parts  of  the  metal  to  100  parts  of  soil. 
(5)  The  influence  of  Zinc  Salts  on  Wheat. 
Magnesium  salts  applied  to  wheat  having  shown,  in  previous 
years,  striking  results,  it  was  determined  to  try,  in  1909, 
experiments  with  another  metal  of  this  same  group,  zinc  being 
selected  for  the  purpose.  The  salts  employed  were  the  oxide, 
chloride,  sulphate,  and  carbonate,  each  application  supplying 
the  same  amount  of  the  metal  zinc,  viz.,  ‘04  per  cent.,  or  ‘04 
parts  to  100  parts  of  soil,  and  the  salts  being  mixed  intimately 
with  the  whole  bulk  of  the  soil. 
After  a first  sowing  in  December,  which  was  spoilt  by  frost 
and  snow,  a resowing  on  January  18,  1909,  was  made.  In  all 
cases  of  application  of  zinc  salts  germination  was  distinctly 
retarded,  though,  eventually,  from  seven  to  eleven  of  the  twelve 
seeds  sown  came  up.  By  April  25  the  use  of  the  soluble  salts 
— the  chloride  and  sulphate — had  produced  decidedly  harmful 
effects,  as  shown  in  the  crop  when  compared  with  the  untreated. 
The  insoluble  salts — the  oxide  and  carbonate — while  also  show- 
ing injury,  did  not  do  so  to  the  same  extent.  The  injury  was 
principally  seen  in  the  absence  of  tillering,  and  in  the  weakness 
of  the  straw.  From  this  they  never  recovered,  and  it  suffices 
to  say  that  it  was  shown  that  zinc  to  the  amount  of  '04  per  cent, 
of  the  metal,  in  a soil,  will  exert  a toxic  effect,  and  that  the 
injury  is  the  greater  with  the  more  soluble  salts.  The  experi- 
ment will  be  continued,  using  zinc  in  smaller  amounts. 
(c)  The  influence  of  Iron  and  Manganese  on  Barley. 
Other  workers  besides  ourselves  at  Woburn  having  shown 
that  iron  and  manganese  salts,  used  in  small  quantities,  have 
exercised  a stimulating  effect  upon  cereal  crops,  the  present 
series  of  experiments  was  started  in  1909  with  the  object  of 
ascertaining  whether  altering  the  ratio  of  one  class  of  salt  to 
