The  fern  is  a  remarkably  stable  type  of  vegetation.  The  earliest
forms,  like  the  Cyclopteris  Hibemica  of  Forbes  from  the  Old  Bed
Sandstone,  agrees  in  all  comparable  points  with  the  recent  plants ;
and  throughout  all  the  intervening  space  no  divergence  in  any  point
of  importance  has  been  detected.
II.  No  group  of  fossil  plants  can  more  fully  illustrate  the  imper-
fect materials  with  which  the  pala^ontological  botanist  has  to  deal
tiian  that  group  which  I  have  united  under  the  name  Calamites^  The
various  parts  of  the  plant — the  root,  the  stem,  the  leaves,  and  the

^  On  the  Structure  of  the  Fruit  of  Calamitst.    Soeman's  Journal  of  Botany,  roL  t.
fia67),  p.  349,  PI.  70.
W.  Comakers— lU  ForeiU  of  the  Coal  Period.      80S


frntt— lutYe  been  formed  into  nnmeitnu  generm,  which  ha^e  been
referred  to  widely  different  poritions  in  the  vegetable  kingdom.
Considerable  diverrity  of  stmotare  is  to  be  foand  in  uoee  stems
which  are  referred  to  Catamites.  I  shall  ask  yonr  attention  to  one  of
these  forms  which  I  have  described,^  and  which  is  beautifully  iUns-
trated  by  a  series  of  drawings,  recently  published,  of  specimens  in  Mr.
Binney's  collection.*  This  stem  was  composed  of  a  centred  medulla
surrounded  by  a  woody  cylinder,  composed  entirely  of  scalariform
vessels  and  a  thin  cortical  layer.  The  medulla  penetrated  the  woody
cylinder  by  a  series  of  regular  wedges,  which  were  continued,  as
delicate  lamiuBd  of  one  or  two  cells  in  thickness,  to  the  cortical  layer.
