﻿Systematic 
  Atavism 
  649 
  

  

  to 
  be 
  of 
  rare 
  occurrence, 
  as 
  I 
  have 
  not 
  suc- 
  

   ceeded 
  in 
  getting 
  any 
  repetition 
  by 
  prolonged 
  

   culture. 
  

  

  Species, 
  which 
  generally 
  bear 
  their 
  leaves 
  in 
  

   whorls, 
  are 
  also 
  subjected 
  to 
  casual 
  atavisms 
  of 
  

   this 
  kind, 
  as 
  for 
  instance 
  the 
  tall 
  European 
  

   horsetail, 
  Equisetum 
  Telmateja, 
  which 
  occasion- 
  

   ally 
  bears 
  cones 
  on 
  its 
  green 
  summer 
  stems. 
  

   Its 
  whorls 
  are 
  changed 
  on 
  the 
  twisted 
  parts 
  into 
  

   clearly 
  visible 
  spirals. 
  The 
  ironwood 
  or 
  Cas- 
  

   uarina 
  quadrivalvis 
  is 
  sometimes 
  observed 
  to 
  

   produce 
  the 
  same 
  anomaly 
  on 
  its 
  smaller 
  lateral 
  

   branches. 
  

  

  Coming 
  now 
  to 
  the 
  discussion 
  of 
  the 
  way 
  in 
  

   which 
  the 
  twisting 
  is 
  the 
  result 
  of 
  the 
  spiral 
  dis- 
  

   position 
  of 
  the 
  leaves, 
  we 
  may 
  consider 
  this 
  ar- 
  

   rangement 
  on 
  stems 
  in 
  the 
  adult 
  state. 
  These 
  

   at 
  once 
  show 
  the 
  spiral 
  line 
  and 
  it 
  is 
  easy 
  to 
  fol- 
  

   low 
  this 
  line 
  from 
  the 
  base 
  up 
  to 
  the 
  apex. 
  In 
  

   the 
  most 
  marked 
  cases 
  it 
  continues 
  without 
  in- 
  

   terruption, 
  not 
  rarely 
  however, 
  ending 
  in 
  a 
  

   whorl 
  of 
  three 
  leaves 
  and 
  a 
  subsequent 
  straight 
  

   internode, 
  of 
  which 
  there 
  may 
  even 
  be 
  two 
  or 
  

   three. 
  The 
  spiral 
  exhibits 
  the 
  basal 
  parts 
  of 
  the 
  

   leaves, 
  with 
  the 
  axillary 
  lateral 
  branches. 
  The 
  

   direction 
  of 
  the 
  screw 
  is 
  opposed 
  to 
  that 
  of 
  the 
  

   twisting, 
  and 
  the 
  spiral 
  ribs 
  are 
  seen 
  to 
  cross 
  the 
  

   line 
  of 
  insertion 
  of 
  the 
  leaves 
  at 
  nearly 
  right 
  

   angles. 
  On 
  this 
  line 
  the 
  leaves 
  are 
  nearer 
  

  

  