﻿624 
  Mutations 
  

  

  broom-like 
  variety 
  of 
  the 
  Populus 
  nigra, 
  from 
  

   which 
  it 
  is 
  distinguished 
  by 
  its 
  erect 
  branches 
  

   and 
  other 
  characters 
  of 
  minor 
  importance. 
  It 
  

   is 
  often 
  called 
  the 
  pyramidal 
  or 
  fastigiate 
  

   poplar. 
  Its 
  origin 
  is 
  absolutely 
  unknown 
  and 
  

   it 
  occurs 
  only 
  in 
  the 
  cultivated 
  state. 
  In 
  Italy 
  

   it 
  seems 
  to 
  have 
  been 
  cultivated 
  from 
  the 
  

   earliest 
  historical 
  times, 
  but 
  it 
  was 
  not 
  intro- 
  

   duced 
  into 
  other 
  countries 
  till 
  the 
  eighteenth 
  

   century. 
  In 
  1749 
  it 
  was 
  brought 
  into 
  France, 
  

   and 
  in 
  1758 
  into 
  England, 
  and 
  to-day 
  it 
  

   may 
  be 
  seen 
  along 
  roads 
  throughout 
  cen- 
  

   tral 
  Europe 
  and 
  in 
  a 
  large 
  part 
  of 
  Asia. 
  But 
  

   the 
  most 
  curious 
  fact 
  is 
  that 
  it 
  is 
  only 
  observed 
  

   in 
  staminate 
  specimens 
  ; 
  pistillate 
  trees 
  have 
  not 
  

   been 
  found, 
  although 
  often 
  sought 
  for. 
  This 
  

   circumstance 
  makes 
  it 
  very 
  probable 
  that 
  the 
  

   origin 
  of 
  the 
  broom-like 
  poplar 
  was 
  a 
  sudden 
  

   mutation, 
  producing 
  only 
  one 
  individual. 
  This 
  

   being 
  staminate, 
  it 
  has 
  been 
  propagated 
  ex- 
  

   clusively 
  by 
  cuttings. 
  It 
  is 
  to 
  be 
  admitted, 
  

   however, 
  that 
  no 
  material 
  evidence 
  is 
  at 
  hand 
  

   to 
  prove 
  that 
  it 
  is 
  not 
  an 
  original 
  wild 
  species, 
  

   the 
  pistillate 
  form 
  of 
  which 
  has 
  been 
  lost 
  by 
  

   vegetative 
  multiplication. 
  One 
  form 
  only 
  of 
  

   many 
  dioecious 
  plants 
  is 
  to 
  be 
  found 
  in 
  cultiva- 
  

   tion, 
  as 
  for 
  instance 
  some 
  South 
  American 
  

   species 
  of 
  Ribes. 
  

  

  Total 
  lack 
  of 
  historical 
  evidence 
  concerning 
  

  

  