﻿HERITABLE 
  VARIATIONS 
  MULLER 
  359 
  

  

  are 
  likewise 
  susceptible, 
  and 
  also 
  the 
  larval 
  somatic 
  cells. 
  The 
  

   latter 
  finding, 
  which 
  has 
  recently 
  been 
  announced 
  also 
  by 
  Timofeeff- 
  

   Ressovsky, 
  opens 
  up 
  a 
  whole 
  realm 
  of 
  interesting 
  possibilities 
  in 
  the 
  

   production 
  of 
  mutant 
  areas 
  of 
  the 
  adult 
  body, 
  derived 
  from 
  cells 
  of 
  

   the 
  treated 
  embryo 
  — 
  such 
  effects 
  as 
  might 
  result, 
  for 
  instance, 
  in 
  an 
  

   individual 
  with 
  eyes 
  of 
  different 
  colors, 
  or 
  with 
  parts 
  of 
  the 
  same 
  eye 
  

   different. 
  Casteel 
  has 
  been 
  making 
  an 
  anatomical 
  analysis 
  of 
  these 
  

   latter 
  effects 
  through 
  microscopic 
  sections 
  of 
  the 
  eye. 
  The 
  produc- 
  

   tion 
  of 
  mutations 
  by 
  X 
  rays 
  is 
  thus 
  a 
  general 
  effect 
  for 
  Drosophila, 
  

   obtainable 
  in 
  all 
  kinds 
  of 
  cells 
  in 
  that 
  organism. 
  What, 
  now, 
  of 
  the 
  

   production 
  of 
  the 
  effect 
  on 
  other 
  organisms? 
  

  

  I 
  need 
  not, 
  perhaps, 
  remind 
  the 
  general 
  reader 
  of 
  the 
  fact 
  that 
  all 
  

   the 
  principles 
  of 
  heredity 
  so 
  far 
  discovered 
  in 
  the 
  fruit 
  fly 
  — 
  the 
  favorite 
  

   experimental 
  object 
  of 
  many 
  modern 
  geneticists— 
  have 
  proved 
  appli- 
  

   cable 
  to 
  animals 
  and 
  plants 
  in 
  general. 
  It 
  is 
  more 
  to 
  the 
  point 
  to 
  

   mention 
  that 
  investigators 
  elsewhere, 
  working 
  on 
  other 
  organisms, 
  

   have 
  now 
  reported 
  results 
  of 
  the 
  same 
  kind 
  as 
  those 
  now 
  in 
  question. 
  

   Thus 
  Stadler, 
  at 
  the 
  University 
  of 
  Missouri, 
  was 
  independently 
  

   attempting 
  to 
  induce 
  gene 
  mutations 
  in 
  barley 
  and 
  in 
  corn 
  by 
  means 
  

   of 
  X 
  rays 
  and 
  radium 
  at 
  the 
  same 
  time 
  that 
  I 
  was 
  doing 
  my 
  first 
  

   experiments 
  along 
  these 
  lines 
  on 
  flies, 
  and 
  he 
  has 
  found 
  indubitable 
  

   evidence 
  of 
  the 
  production 
  of 
  gene 
  mutations 
  in 
  monocotyledonous 
  

   plants 
  by 
  both 
  of 
  these 
  means. 
  Following 
  my 
  work 
  on 
  flies, 
  P. 
  W. 
  

   and 
  A. 
  R. 
  Whiting 
  have 
  obtained 
  positive 
  results 
  by 
  the 
  use 
  of 
  X 
  rays 
  

   on 
  wasps. 
  Blakeslee, 
  Buchholtz, 
  and 
  the 
  others 
  of 
  this 
  group 
  have 
  

   a 
  mass 
  of 
  interesting 
  mutation 
  results 
  from 
  X 
  rays 
  and 
  radium 
  applied 
  

   to 
  the 
  Jimson 
  weed. 
  Datura, 
  that 
  extend 
  the 
  findings 
  concerning 
  lethal 
  

   as 
  well 
  as 
  visible 
  mutations 
  to 
  dicotyledonous 
  plants. 
  With 
  these 
  so 
  

   widely 
  separated 
  bits 
  of 
  the 
  living 
  world 
  sampled 
  and 
  all 
  responding 
  

   positively, 
  it 
  is 
  a 
  reckless 
  critic 
  who 
  still 
  would 
  cast 
  a 
  doubt 
  as 
  to 
  the 
  

   probable 
  generality 
  of 
  the 
  phenomenon. 
  

  

  Radium 
  rays, 
  like 
  X 
  rays, 
  produce 
  mutations, 
  as 
  has 
  been 
  shown 
  

   by 
  Hanson 
  and 
  by 
  Stadler. 
  This 
  is 
  because 
  they, 
  too, 
  being 
  short 
  

   wave 
  length 
  high-frequency 
  electromagnetic 
  waves 
  of 
  great 
  energy 
  

   content, 
  release 
  high-speed 
  electrons, 
  and 
  the 
  cosmic 
  rays, 
  which 
  are 
  

   still 
  more 
  extreme 
  in 
  these 
  respects, 
  and 
  so 
  release 
  electrons 
  of 
  still 
  

   higher 
  speed, 
  must 
  necessarily 
  act 
  likewise. 
  For, 
  as 
  Hanson 
  has 
  

   shown 
  in 
  experiments 
  with 
  radium, 
  the 
  number 
  of 
  mutations 
  produced 
  

   depends 
  simply 
  on 
  the 
  number 
  of 
  electrons 
  released 
  and 
  the 
  speed 
  and 
  

   distance 
  they 
  travel 
  (i. 
  e., 
  the 
  total 
  energy 
  of 
  ionization), 
  regardless 
  of 
  

   the 
  source 
  of 
  the 
  electrons. 
  Oliver 
  too, 
  in 
  experiments 
  with 
  X 
  rays 
  

   in 
  our 
  laboratory, 
  has 
  obtained 
  evidence 
  that 
  the 
  number 
  of 
  mutations 
  

   produced 
  is 
  directly 
  proportional 
  to 
  the 
  dosage 
  of 
  radiation 
  used, 
  

   and 
  Stadler's 
  work 
  points 
  in 
  the 
  same 
  direction.' 
  This 
  being 
  true, 
  

   there 
  being 
  no 
  evidence 
  of 
  a 
  minimal 
  or 
  "threshold" 
  dosage, 
  we 
  are 
  

  

  