﻿306 
  T. 
  Holm 
  — 
  Vitality 
  of 
  some 
  Annual 
  Plants. 
  

  

  etate 
  for 
  several 
  years 
  without 
  flowering, 
  if 
  the 
  locality 
  

   becomes 
  inundated.* 
  

  

  It 
  seems 
  then, 
  that 
  this 
  ability 
  to 
  vary 
  among 
  Cyperacem 
  is 
  

   easy 
  to 
  explain, 
  although 
  it 
  may 
  not 
  be 
  a 
  necessary 
  consequence 
  

   in 
  all 
  cases 
  ; 
  our 
  specimens 
  of 
  Cyperus 
  were 
  observed 
  as 
  occur- 
  

   ring 
  together 
  with 
  numerous 
  annual 
  individuals 
  and 
  under 
  the 
  

   very 
  same 
  conditions. 
  

  

  The 
  Graminece 
  may 
  undoubtedly 
  include 
  several 
  other 
  

   species, 
  besides 
  the 
  cultivated 
  ones, 
  mentioned 
  by 
  Hildebrand 
  

   (1. 
  c.) 
  in 
  which 
  this 
  same 
  variation 
  may 
  take 
  23lace. 
  Tragus 
  race- 
  

   mosus 
  Hall, 
  represents 
  at 
  least 
  the 
  same 
  case 
  as 
  that 
  of 
  Cyperus. 
  

   It 
  has 
  always 
  been 
  considered 
  as 
  annual, 
  lately 
  by 
  Dr. 
  Vasey,+ 
  

   although 
  some 
  specimens 
  in 
  U. 
  S. 
  National 
  herbarium 
  prove, 
  

   that 
  it 
  can 
  also 
  occur 
  as 
  perennial. 
  These 
  specimens 
  have 
  

   long 
  stolons 
  above-ground 
  with 
  abundant 
  formation 
  of 
  leafy 
  

   shoots 
  at 
  each 
  node, 
  from 
  where 
  long 
  roots 
  are 
  also 
  developed. 
  

   A 
  part 
  of 
  a 
  stolon 
  has 
  been 
  illustrated 
  in 
  plate 
  X, 
  fig. 
  2, 
  

   where 
  we 
  see 
  not 
  only 
  the 
  crowded 
  shoots, 
  but 
  also 
  a 
  secon- 
  

   dary 
  formation 
  stolons 
  (S). 
  All 
  these 
  shoots 
  were 
  developed 
  

   in 
  the 
  axils 
  of 
  leaves, 
  belonging 
  to 
  the 
  stolons, 
  and 
  they 
  

   showed 
  besides 
  the 
  proper 
  leaves 
  also 
  the 
  characteristic 
  pro- 
  

   phyllum 
  (fig. 
  3). 
  This 
  small 
  leaf 
  had 
  a 
  rather 
  unusual 
  shape 
  

   than 
  otherwise 
  observed 
  ; 
  it 
  was 
  not 
  only 
  distinctly 
  bicarinate, 
  

   but 
  showed 
  at 
  its 
  apex 
  two 
  long 
  teeth, 
  corresponding 
  to 
  those 
  

   of 
  an 
  ordinary 
  palet 
  (fig. 
  4). 
  A 
  transverse 
  section 
  (fig. 
  5) 
  of 
  

   the 
  prophyllum 
  shows 
  the 
  prominent 
  keels 
  and 
  the 
  very 
  thin 
  

   margins, 
  besides 
  the 
  presence 
  of 
  not 
  only 
  two, 
  but 
  even 
  six 
  

   nerves, 
  those 
  of 
  the 
  keels 
  being 
  the 
  strongest. 
  

  

  This 
  manner 
  of 
  growth 
  seems 
  to 
  be 
  rather 
  common 
  in 
  

   North 
  American 
  Gramince, 
  especially 
  those, 
  which 
  ramify, 
  ' 
  

   and 
  there 
  is 
  no 
  doubt 
  that 
  under 
  favorable 
  conditions 
  they 
  

   might 
  change 
  their 
  habit 
  from 
  annual 
  to 
  perennial 
  or 
  at 
  least 
  

   biennial. 
  

  

  The 
  Crucifero3, 
  which 
  include 
  representatives 
  of 
  all 
  the 
  three 
  

   types 
  of 
  growth, 
  are, 
  as 
  mentioned 
  above, 
  quite 
  apt 
  to 
  vary 
  in 
  

   a 
  similar 
  manner. 
  The 
  genus 
  Arabis 
  is 
  very 
  instructive 
  in 
  

   this 
  regard, 
  as 
  for 
  instance 
  A. 
  dentata 
  Torr. 
  et 
  Gr., 
  of 
  which 
  

   the 
  lower 
  part 
  of 
  a 
  perennial 
  specimen 
  has 
  been 
  figured 
  on 
  

   Plate 
  X, 
  fig. 
  7, 
  which 
  shows 
  the 
  character 
  of 
  a 
  biennial 
  in 
  a 
  

   perennial 
  form. 
  We 
  see 
  here 
  a 
  leafy 
  shoot 
  terminating 
  the 
  

   main 
  axis, 
  from 
  the 
  leaves 
  of 
  which 
  fiowering 
  stems 
  will 
  be 
  

   developed 
  next 
  year. 
  We 
  see 
  further, 
  that 
  the 
  base 
  of 
  this 
  

   shoot 
  is 
  surrounded 
  by 
  now 
  faded 
  leaves, 
  merely 
  indicated 
  by 
  

   the 
  petioles, 
  and 
  from 
  the 
  axils 
  of 
  which 
  proceed 
  the 
  ascend- 
  

   ing 
  flowering 
  stems 
  of 
  the 
  year. 
  

  

  * 
  Compare 
  : 
  Bull, 
  de 
  la 
  Societe 
  bocan. 
  de 
  France. 
  1860. 
  p. 
  1S6. 
  

   f 
  Geo. 
  Vasey 
  : 
  Grasses 
  of 
  the 
  Southwest, 
  Part 
  I, 
  1890. 
  (Bull, 
  of 
  U. 
  S. 
  Dept. 
  

   of 
  Agriculture). 
  

  

  