We  have  in  the  Introductory -Chapter  taken  notwe  of  the
great  proportion  of  space  occupied  by  the  Mosses  in  the
temperate  and  colder  zones  of  the  earth,  finding  that  they
abound  to  such  an  extent  as  to  eradicate,  in  many  instances,
the  grasses  and  other  plants  amid  which  they  grow.  In
general,  wherever  moisture  and  shade  is  afforded,  we  find


GEOGRAPHICAL   DISTRIBUTION.  45

one  or  another  species,  according  to  the  season  of  the  year,
or  the  nature  of  the  soil,  or  other  material  on  which  they
thrive.     AVith  reference  to  this  latter  point  there  is  con-
siderable variety  among  Mosses,  though  not  so  much  as  we
find  among  higher  plants.     Some  species  prefer  clay,  and
others  peat ;  one  genus  affects  sandstone,  and  another  cal-
careous rocks,  while  several  are  found  chiefly  on  particular
species  of  trees.    Mr.  Spruce,  in  his  interesting  paper  on  the
"  Mosses  of  Teesdale,"  published  in  the  Transactions  of  the
Botanical  Society  of  Edinburgh,  observed  however  that  in
that  district  "  very  few  of  the  Mosses  were  absolutely  con-
fined" to  either  the  basaltic  or  limestone  clifl's  of  which  it
is  composed.     In  speaking  of  the  varied  localities  in  which
particular  genera  or  species  are  found,   Drs.  Hooker  and
Taylor,  in  the  preface  to  their  interesting  '  IMuscologia  Bri-
tannica,^  make  the  following  remarks  : — "  One  curious  little
plant  is  found  only  on  the  perpendicular  faces  of  the  pui'e
white  chalk-pits  that  abound  so  much  in  Kent  and  Sussex.
