542 
PRODUCTION  OF  CORK. 
of  cork.  Although  this  useful  substance  exists  in  varying  quan- 
tity in  the  bark  of  all  phanerogamous  plants  and  in  several 
cryptogamous,  yet  for  commercial  purposes  it  is  wholly  pro- 
cured from  two  species  of  oak,  Quercus  occidentalism  growing  in 
the  south-west  of  France  and  in  Portugal,  and  from  Quercus 
Suber  (the  cork-tree,)  growing  in  the  south-east  of  France,  in 
Italy,  in  Algeria,  and  in  the  isles  of  the  Mediterranean.  The 
acorns  of  the  former  species  take  two  years  to  ripen.  In  1859 
M.  C.  de  Candolle,  while  staying  in  Algeria,  studied  the  devel- 
opement  of  the  bark  of  the  latter  species.  It  is  composed  of 
four  layers — the  epidermis,  the  corky  envelope,  the  cellular  en- 
velope, and  the  liber  which  covers  the  soft  wood.  These  four 
parts  increase  independently  of  each  other  year  by  year.  In 
the  third  or  fourth  year  the  epidermis,  having  attained  the 
limits  of  its  elasticity,  splits  longitudinally,  and  a  marked  change 
takes  place  in  the  corky  envelope,  which  gradually  takes  up  the 
appearance  of  true  cork :  new  layers  are  produced,  and  the 
transformation  of  cellulose  into  cork  steadily  goes  on.  The 
cork  thus  naturally  developed  has  no  commercial  value.  It  is 
termed  "male;"  and  the  first  act  (demasclage)  of  the  cultivator 
is  to  separate  it  from  the  trunk,  which  thus  leaves  exposed  the 
liber,  termed  '«  mother."  The  tree  is  then  left  to  itself,  and 
the  cork  begins  to  grow  again,  whilst  the  sap  is  flowing  in  con- 
sequence of  the  exposure  of  the  liber.  If  a  trunk  left  in  this 
state  for  several  months  be  cut  down,  in  the  section  a  ring  of 
cork  will  be  found  formed  in  the  interior  of  the  "mother,"  at  a 
variable  distance  from  the  surface  of  the  trunk  All  the  ex- 
terior portion  of  the  "mother"  is  dead,  and  splits  as 
the  tree  grows,  and  the  interior  portion  (new  cork,  termed  "  fe- 
male ")  is  developed.  This  "  female  "  cork  grows  in  the  same 
manner  as  the  "  male,"  that  is,  by  the  addition  of  annual 
layers  on  the  internal  surface ;  but  it  is  much  finer  and  more 
elastic,  and  is  the  cork  of  commerce.  These  various  stages  of 
growth  are  exhibited  in  a  series  of  beautiful  plates.  In  the 
course  of  his  researches  M.  de  Candolle  was  led  to  observe  the 
importance  of  the  desiccation  of  the  "  mother,"  and  to  infer 
that,  in  proportion  as  this  desiccation  could  be  hastened,  so 
much  sooner  would  fresh  layers  of  cork  be  produced.  This  idea 
he  found  to  be  correct.    He  observed  several  trees  in  which 
