554  Relations  of  Plants  to  Distilled  Water.  {A£c£X'r Pi9i?* 
or  five  days  a  splendid  lot  of  vigorous,  uniform  seedlings  which  have 
serviceably  straight  radicles  about  2  inches  long  with  no  laterals  yet 
formed  is  obtained  by  this  method ;  such  seedlings  are  well  adapted, 
both  by  their  character  and  their  accommodation  to  an  aqueous 
medium,  for  solution-culture  work.  At  this  stage  the  plumules  have 
grown  to  about  one-half  inch  in  length,  and  the  plants  are  now  ready 
for  transfer  to  the  culture  medium,  an  operation  which  is  easily  and 
quickly  done.  This  method  of  germination  recommends  itself  both 
by  reason  of  its  simplicity  and  ease  of  operation  and  the  certainty  of 
securing  excellent  results.  In  the  transfer  process  from  the  germi- 
nating pan  to  the  culture  medium,  the  entire  seedling  was  always  im- 
mersed and  carefully  rinsed  in  once-distilled  and  again  in  twice-dis- 
tilled water;  by  this  means  the  roots  became  free  of  any  adhering 
impurities. 
As  containers  for  the  cultures,  ordinary  glass  tumblers  were  used, 
the  sides  of  which  were  covered  with  black  paper  to  prevent  algal 
growth  and  the  top  covered  with  perforated  paraffin  paper.  (For  a 
complete  description  and  illustration  of  the  method  see  the  paper  by 
McCool,  '13.)  Ten  plants  were  grown  in  most  cases  in  each  tumbler ; 
exceptions  to  that  number  will  be  noted  in  each  cas»e  when  the  series 
are  discussed  in  detail.  Galvanized  iron  wire  supports  were  used  to 
hold  the  plants  upright  when  the  seedlings  had  attained  sufficient  size 
to  require  them. 
In  all  cases  doubly  distilled  water  was  used,  the  second  distillation 
being  carried  out  in  the  laboratory  with  KMn04  added  to  the  once- 
distilled  water  to  oxidize  any  organic  matter  that  might  be  present. 
Conductivity  tests  of  this  water  showed  it  to  possess  a  specific  con- 
ductivity of  2.064  X  io~6.  The  nutrient  solution  used  was  that  of 
Pfeffer,  redistilled  water  being  the  solvent  for  the  necessary  salts. 
Each  tumbler  was  filled  to  a  convenient  level  with  either  the  water 
or  the  full  nutrient  solution  as  the  case  might  be,  approximately  250 
Cc.  being  required.  To  replace  transpiration  loss,  doubly  distilled 
water  was  added  as  needed. 
In  the  early  days  of  conductivity  work  on  solutions,  measure- 
ments could  be  made  only  by  means  of  a  continuous  current.  Be- 
cause of  the  resulting  polarization  effects,  however,  the  resistance  of 
the  solution  increased  to  such  an  extent  as  to  introduce  serious  errors 
into  the  results.  But  thanks  to  the  classical  work  of  Kohlrausch 
and  others,  the  alternating  current  method  was  devised  and  per- 
fected, whereby  the  determinations  became  practically  independent  of 
