﻿Elementary 
  Species 
  in 
  Nature 
  53 
  

  

  ula, 
  Spergula 
  media 
  and 
  salina 
  and 
  many 
  other 
  

   pairs 
  of 
  allied 
  species 
  have 
  differentiating 
  char- 
  

   acters 
  of 
  the 
  same 
  value 
  as 
  those 
  of 
  the 
  element- 
  

   ary 
  species 
  of 
  Draba 
  verna. 
  Filago, 
  Plantago, 
  

   Carex, 
  Ficaria 
  and 
  a 
  long 
  series 
  of 
  other 
  genera 
  

   afford 
  proofs 
  of 
  the 
  same 
  close 
  relation 
  be- 
  

   tween 
  smaller 
  and 
  larger 
  groups 
  of 
  species. 
  The 
  

   European 
  frost-weeds 
  or 
  Helianthemum 
  in- 
  

   clude 
  a 
  group 
  of 
  species 
  which 
  are 
  so 
  closely 
  al- 
  

   lied, 
  that 
  ordinary 
  botanical 
  descriptions 
  are 
  

   not 
  adequate 
  to 
  give 
  any 
  idea 
  of 
  their 
  differen- 
  

   tiating 
  features. 
  It 
  is 
  almost 
  impossible 
  to 
  

   determine 
  them 
  by 
  means 
  of 
  the 
  common 
  ana- 
  

   lytical 
  keys. 
  They 
  have 
  to 
  be 
  gathered 
  from 
  

   their 
  various 
  native 
  localities 
  and 
  cultivated 
  

   side 
  by 
  side 
  in 
  the 
  garden 
  to 
  bring 
  out 
  their 
  

   differences. 
  Among 
  the 
  species 
  of 
  France, 
  ac- 
  

   cording 
  to 
  Jordan, 
  Helianthemum 
  polifolium, 
  

   H. 
  apenninum, 
  H. 
  pilosum 
  and 
  H. 
  pulverulen- 
  

   tum 
  are 
  of 
  this 
  character. 
  

  

  A 
  species 
  of 
  cinquefoil, 
  Potentilla 
  Tormen- 
  

   tilla, 
  which 
  is 
  distinguished 
  by 
  its 
  quaternate 
  

   flowers, 
  occurs 
  in 
  Holland 
  in 
  two 
  distinct 
  types, 
  

   which 
  have 
  proved 
  constant 
  in 
  my 
  cultural 
  exper- 
  

   iments. 
  One 
  of 
  them 
  has 
  broad 
  petals, 
  meeting 
  

   together 
  at 
  the 
  edges, 
  and 
  constituting 
  a 
  round- 
  

   ed 
  saucer 
  without 
  breaks. 
  The 
  other 
  has 
  nar- 
  

   row 
  petals, 
  which 
  are 
  strikingly 
  separated 
  from 
  

   one 
  another 
  and 
  show 
  the 
  sepals 
  between 
  them. 
  

  

  