﻿. 
  1890.] 
  BOTANICAL 
  GAZETTE. 
  ' 
  5 
  

  

  nearer 
  to 
  Botrychium 
  than 
  do 
  the 
  Marattiacece, 
  although 
  in 
  

   some 
  other 
  respects 
  this 
  is 
  not 
  the 
  case. 
  While 
  the 
  tibro- 
  

   vascular 
  bundles 
  of 
  Ophioglossum 
  are 
  collaterar" 
  (which 
  is 
  

   also 
  true 
  of 
  Osmunda^') 
  those 
  of 
  Botrychium 
  are 
  concentric, 
  

   this 
  being 
  particularly 
  noticeable 
  in 
  the 
  larger 
  species, 
  such 
  

   as 
  B. 
  ternatum 
  and 
  B. 
  Virginianum. 
  In 
  these 
  larger 
  species, 
  

   too, 
  there 
  is 
  some 
  slight 
  trace 
  of 
  a 
  hypoderma 
  distinct 
  from 
  

   the 
  rest 
  of 
  the 
  ground 
  tissue, 
  and 
  the 
  bundle-sheath 
  is 
  pretty 
  

   well 
  detined. 
  

  

  As 
  has 
  been 
  shown, 
  too, 
  while 
  in 
  B. 
  simplex 
  the 
  leaf 
  is 
  

  

  Vi 
  

  

  M 
  

  

  and 
  Filices. 
  

  

  If 
  we 
  assume 
  Ophioglossum 
  to 
  be 
  the 
  higher 
  form 
  (being 
  

   most 
  strongly 
  eusporangiate), 
  it 
  is 
  certainly 
  difficult 
  to 
  ac- 
  

   count 
  for 
  the 
  gradual 
  simplification 
  of 
  the 
  tissues 
  as 
  we 
  pass 
  

   from 
  the 
  Filices 
  through 
  Botrychium 
  or 
  the 
  Marattiaceaj. 
  

   Such 
  a 
  simplification 
  can 
  not 
  be 
  accounted 
  for 
  from 
  the 
  habits 
  

   of 
  the 
  plant, 
  as 
  it 
  is 
  neither 
  an 
  aquatic 
  nor 
  a 
  parasite. 
  

  

  The 
  greatest 
  difficulty, 
  however, 
  it 
  seems 
  to 
  me, 
  in 
  regard- 
  

   ing 
  the 
  Hymenophyllaceae 
  as 
  primitive 
  forms 
  as 
  compared 
  

   with 
  the 
  Marattiaceai 
  and 
  Ophioglosseae 
  is 
  the 
  increase 
  in 
  the 
  

   size 
  of 
  the 
  prothallium 
  as 
  we 
  go 
  from 
  the 
  former 
  to 
  the 
  latter. 
  

   Bower'' 
  tries 
  to 
  explain 
  this 
  by 
  assuming 
  that 
  the 
  size 
  and 
  

   complexity 
  of 
  the 
  prothallium 
  are 
  correlated 
  with 
  the 
  increas- 
  

   ing 
  complexity 
  of 
  the 
  sporophyte, 
  and 
  like 
  it 
  due 
  to 
  the 
  

   change 
  from 
  a 
  semi-aquatic 
  to 
  a 
  purely 
  terrestrial 
  habit. 
  

  

  There 
  are 
  two 
  objections 
  to 
  this 
  view 
  : 
  First, 
  if 
  we 
  admit 
  

   that 
  the 
  cycads 
  are 
  related 
  to 
  the 
  Marattiaceae 
  (which 
  Bower 
  

   seems 
  to 
  think 
  very 
  probable), 
  we 
  must 
  suppose 
  a 
  reduction 
  

   of 
  the 
  prothallium 
  again 
  to 
  produce 
  the 
  heterosporous 
  forms 
  

   that 
  must 
  have 
  intervened. 
  That 
  there 
  should 
  be 
  an 
  increase 
  

   in 
  the 
  size 
  of 
  the 
  prothallium 
  up 
  to 
  a 
  certain 
  point, 
  keeping 
  

   pace 
  with 
  the 
  development 
  of 
  the 
  sporophyte, 
  and 
  then 
  a 
  

   retrogression, 
  is 
  difficult 
  to 
  understand, 
  and 
  is 
  certainly 
  im- 
  

   probable. 
  If 
  on 
  the 
  other 
  hand 
  we 
  admit 
  that 
  the 
  Marattia- 
  

   ceae 
  are 
  primitive 
  forms, 
  allied, 
  perhaps, 
  to 
  Ophioglossum, 
  

   the 
  massive 
  character 
  of 
  the 
  oophyte 
  is 
  easily 
  comprehensi- 
  

   ble, 
  and 
  the 
  possible 
  derivation 
  of 
  the 
  cycads 
  from 
  them 
  

   could 
  then 
  be 
  understood 
  by 
  assuming 
  a 
  series 
  ending 
  in 
  

   some 
  heterosporous 
  form 
  leading 
  up 
  to 
  the 
  former. 
  ^^ 
  

  

  i« 
  De 
  Bary, 
  op. 
  c. 
  pp. 
  321 
  , 
  364. 
  

   " 
  De 
  Bary, 
  1. 
  c. 
  

   is 
  Op. 
  cit., 
  p. 
  370. 
  

  

  the 
  view"(^/ 
  V^n'^f 
  *^ 
  ^^*' 
  possibly 
  Isoetes 
  may 
  be 
  such 
  a 
  form, 
  and 
  this 
  seems 
  to 
  be 
  also 
  

  

  