﻿Systematic 
  Atavism 
  633 
  

  

  allied 
  species. 
  It 
  brings 
  before 
  us, 
  and 
  empha- 
  

   sizes 
  the 
  importance 
  of 
  the 
  conception 
  of 
  the 
  

   so-called 
  unit-characters. 
  

  

  The 
  primrose 
  will 
  serve 
  as 
  an 
  example. 
  In 
  

   the 
  second 
  lecture 
  we 
  have 
  seen 
  that 
  the 
  old 
  

   species 
  of 
  Linnaeus, 
  the 
  Primula 
  veris, 
  was 
  

   split 
  up 
  by 
  Jacquin 
  into 
  three 
  smaller 
  ones, 
  

   which 
  are 
  called 
  P. 
  officinaMs, 
  P. 
  elatior 
  and 
  P. 
  

   acaulls. 
  From 
  this 
  systematic 
  treatment 
  we 
  

   can 
  infer 
  that 
  these 
  three 
  forms 
  are 
  assumed 
  to 
  

   be 
  derived 
  from 
  a 
  common 
  ancestor. 
  Now 
  two 
  

   of 
  them 
  bear 
  their 
  flowers 
  in 
  bracted 
  whorls, 
  

   condensed 
  into 
  umbels 
  at 
  the 
  summits 
  of 
  a 
  scape. 
  

   The 
  scapes 
  themselves 
  are 
  inserted 
  in 
  the 
  axils 
  

   of 
  the 
  basal 
  leaves, 
  and 
  produce 
  the 
  flowers 
  

   above 
  them. 
  In 
  the 
  third 
  species, 
  Primula 
  

   acaulis, 
  this 
  scape 
  is 
  lacking 
  and 
  the 
  flowers 
  are 
  

   inserted 
  singly 
  in 
  the 
  axils 
  on 
  long 
  slender 
  

   stalks. 
  For 
  this 
  reason 
  the 
  species 
  is 
  called 
  

   acaulescent, 
  indicating 
  that 
  it 
  has 
  no 
  other 
  

   stem 
  than 
  the 
  subterranean 
  rootstock. 
  But 
  on 
  

   closer 
  inspection 
  we 
  observe 
  that 
  the 
  flower- 
  

   stalks 
  are 
  combined 
  into 
  little 
  groups, 
  each 
  

   group 
  occupying 
  the 
  axil 
  of 
  one 
  of 
  the 
  basal 
  

   leaves. 
  This 
  fact 
  at 
  once 
  points 
  to 
  an 
  analogy 
  

   with 
  the 
  umbellate 
  allies, 
  and 
  induces 
  us 
  to 
  ex- 
  

   amine 
  the 
  insertion 
  of 
  the 
  flowers 
  more 
  crit- 
  

   ically. 
  In 
  doing 
  so 
  we 
  find 
  that 
  they 
  are 
  united 
  

   at 
  their 
  base 
  so 
  as 
  to 
  constitute 
  a 
  sessile 
  umbel. 
  

  

  