﻿Experimental 
  Pedigree-Cultures 
  573 
  

  

  that 
  this 
  theory 
  of 
  natural 
  selection 
  leaves 
  the 
  

   question 
  as 
  to 
  how 
  the 
  changes 
  themselves 
  are 
  

   brought 
  about, 
  quite 
  undecided. 
  There 
  are 
  two 
  

   possibilities, 
  and 
  both 
  have 
  been 
  propounded 
  by 
  

   Darwin. 
  One 
  is 
  the 
  accumulation 
  of 
  the 
  slight 
  

   deviations 
  of 
  fluctuating 
  variability, 
  the 
  other 
  

   consists 
  of 
  successive 
  sports 
  or 
  leaps 
  taking 
  

   place 
  in 
  the 
  same 
  direction. 
  

  

  In 
  further 
  lectures 
  a 
  critical 
  comparison 
  of 
  

   the 
  two 
  views 
  will 
  be 
  given. 
  To-day 
  I 
  have 
  only 
  

   to 
  show 
  that 
  the 
  mutations 
  of 
  the 
  evening-prim- 
  

   roses, 
  though 
  sudden, 
  comply 
  with 
  the 
  demands 
  

   made 
  by 
  Darwin 
  as 
  to 
  the 
  form 
  of 
  variability 
  

   which 
  is 
  to 
  be 
  accepted 
  as 
  the 
  cause 
  of 
  evolution 
  

   and 
  as 
  the 
  origin 
  of 
  species. 
  

  

  Some 
  of 
  my 
  new 
  types 
  are 
  stouter 
  and 
  others 
  

   weaker 
  than 
  their 
  parents, 
  as 
  shown 
  by 
  gigas 
  

   and 
  albida. 
  Some 
  have 
  broader 
  leaves 
  and 
  

   some 
  narrower, 
  lata 
  and 
  oblonga. 
  Some 
  have 
  

   larger 
  flowers 
  (gigas) 
  or 
  deeper 
  yellow 
  ones 
  

   (rubrinervis) 
  , 
  or 
  smaller 
  blossoms 
  (scintillans), 
  

   or 
  of 
  a 
  paler 
  hue 
  (albida). 
  In 
  some 
  the 
  cap- 
  

   sules 
  are 
  longer 
  (rubrinervis), 
  or 
  thicker 
  

   (gigas), 
  or 
  more 
  rounded 
  (lata), 
  or 
  small 
  (ob- 
  

   longa), 
  and 
  nearly 
  destitute 
  of 
  seeds 
  (brevi- 
  

   stylis). 
  The 
  unevenness 
  of 
  the 
  surface 
  of 
  the 
  

   leaves 
  may 
  increase 
  as 
  in 
  lata, 
  or 
  decrease 
  as 
  in 
  

   laevifolia. 
  The 
  tendency 
  to 
  become 
  annual 
  pre- 
  

   vails 
  in 
  rubrinervis, 
  but 
  gigas 
  tends 
  to 
  become 
  

  

  