﻿304 
  T. 
  Holm 
  — 
  Vitality 
  of 
  some 
  Annual 
  Plants. 
  

  

  Art. 
  XX 
  YIII. 
  — 
  On 
  the 
  Vitality 
  of 
  some 
  Annual 
  Plants 
  : 
  by 
  

   Theo. 
  Holm. 
  (With 
  Plate 
  X.) 
  

  

  The 
  curious 
  fact, 
  that 
  there 
  may 
  be 
  individuals 
  of 
  annual 
  

   species 
  of 
  which 
  the 
  life-time 
  is 
  not 
  limited 
  merely 
  to 
  one 
  

   year, 
  has 
  been 
  noticed 
  by 
  several 
  botanists. 
  Exceptions 
  of 
  that 
  

   kind 
  often 
  seem 
  to 
  be 
  nearly 
  accidental, 
  but 
  in 
  most 
  cases 
  they 
  

   are, 
  however, 
  to 
  be 
  considered 
  as 
  due 
  to 
  certain 
  external 
  fac- 
  

   tors, 
  as 
  for 
  instance 
  climate 
  and 
  soil 
  or 
  cultivation. 
  Indeed, 
  

   the 
  number 
  is 
  not 
  very 
  small 
  of 
  the 
  species 
  in 
  which 
  a 
  fluctua- 
  

   tion 
  has 
  been 
  observed 
  from 
  being 
  annual 
  to 
  perennial 
  or 
  at 
  

   least 
  biennial 
  in 
  a 
  modified 
  sense, 
  as 
  well 
  as 
  of 
  those 
  for 
  which 
  

   similar 
  intergradation-forms 
  have 
  been 
  recorded 
  between 
  the 
  

   biennial 
  on 
  the 
  one 
  side 
  and 
  the 
  annual 
  and 
  perennial 
  ones 
  

   on 
  the 
  other. 
  

  

  Irmisch*" 
  mentions 
  for 
  instance, 
  that 
  Eckinospermum 
  Lap- 
  

   pula. 
  which 
  is 
  usually 
  biennial 
  may 
  occur 
  as 
  annual, 
  having 
  al- 
  

   ready 
  developed 
  the 
  flowers 
  in 
  the 
  first 
  year 
  ; 
  he 
  observed 
  that 
  

   the 
  same 
  is 
  true 
  in 
  the 
  case 
  of 
  Hyoscyamus 
  niger, 
  of 
  which 
  

   even 
  the 
  annual 
  form 
  has 
  been 
  described 
  as 
  a 
  proper 
  species 
  

   (H. 
  agrestis) 
  since 
  it 
  is 
  very 
  different 
  in 
  habit 
  from 
  the 
  

   biennial 
  type. 
  The 
  same 
  author 
  has 
  also 
  observed, 
  that 
  

   Hypericum 
  humifusum 
  and 
  2Ialva 
  neglecta 
  may 
  occur 
  as 
  

   both 
  annual 
  and 
  perennial. 
  Seclum 
  annuum, 
  which 
  has 
  been 
  

   described 
  as 
  annual 
  by 
  Hartman, 
  Areschoug 
  and 
  Blytt, 
  was 
  

   observed 
  by 
  "Warmingf 
  to 
  be 
  biennial, 
  and 
  even 
  that 
  this 
  

   seemed 
  to 
  be 
  the 
  normal 
  for 
  this 
  plant. 
  

  

  Hildebrand^: 
  enumerates 
  several 
  species, 
  which, 
  although 
  they 
  

   occur 
  under 
  widely 
  different 
  conditions 
  in 
  both 
  hemispheres, 
  

   nevertheless 
  seem 
  to 
  be 
  constant 
  as 
  to 
  their 
  life-duration 
  and 
  

   habit; 
  such 
  species 
  for 
  example 
  are 
  the 
  annual 
  Polygonum 
  

   aviculare, 
  Erigeron 
  Canadensis, 
  Palaver 
  Phasas, 
  etc., 
  while 
  

   of 
  perennials 
  Thymus 
  serpyllum, 
  Verbena 
  officinalis, 
  Urtica 
  

   dioica, 
  etc. 
  He 
  enumerates 
  on 
  the 
  other 
  hand 
  several 
  other 
  

   species, 
  which 
  show 
  a 
  tendency 
  to 
  vary 
  from 
  annual 
  to 
  bien- 
  

   nial, 
  among 
  which 
  are 
  many 
  Cruciferos; 
  Composites 
  and 
  culti- 
  

   vated 
  Graminece, 
  besides 
  some 
  usually 
  biennial 
  species, 
  which 
  

   may 
  occur 
  as 
  perennials, 
  as 
  for 
  instance 
  some 
  CrucifercB^ 
  Urn,- 
  

   belliferw, 
  Papilionacece, 
  etc. 
  Similar 
  aberrant 
  forms 
  are 
  evi- 
  

   dently 
  far 
  from 
  rare 
  in 
  this 
  country, 
  though 
  the 
  author 
  has 
  not 
  

  

  * 
  Thilo 
  Irmisch: 
  Zur 
  Morphologie 
  der 
  monocot. 
  Kuollen 
  und 
  Zwiebelge- 
  

   wachse, 
  1850, 
  p. 
  211. 
  

  

  | 
  Kug. 
  Warming 
  : 
  Om 
  Skudbygning. 
  Overvintring 
  og 
  Foryngelse. 
  (Xaturhist. 
  

   Forenings 
  Festskrift, 
  1SS4, 
  p. 
  16.) 
  

  

  X 
  Fr. 
  Hildebrand: 
  Die 
  Lebensdauer 
  und 
  Yegetationsweise 
  der 
  Pflauzen. 
  ihre 
  

   Ursachen 
  und 
  ihre 
  Entwickelung. 
  (Engler's 
  Botanische 
  Jahrbucher. 
  vol. 
  ii, 
  1881, 
  

   p. 
  51.) 
  

  

  