424 
doubt  dwell  upon  particulars  of  which  you  are  more  or  less  fami- 
liar, but  I trust  that  the  interest  will  be  worth  the  short  while 
taken. 
No  two  species  of  trees  produce  wood  of  exactly  the  same  struc- 
ture. There  is  a great  variation  in  woods  of  the  same  species,  in 
fact  a distinct  study  in  each  separate  piece. 
Examine  almost  any  piece  of  wood,  and  in  a general  way  we 
find  it  composed  of  small  cells  of  various  kinds,  usually  long  and 
tubular,  running  lengthwise,  and  adhering  to  each  other  more  or 
less  strongly.  These  cells  have  had  special  uses  in  the  life  of  the 
tree,  some  were  for  conducting  crude  sap  from  the  roots  to  the 
crown,  others  acting  as  storehouses  for  digested  plant  food  and 
still  others  have  long  acted  merely  for  strengthening  the  tree 
and  holding  it  together.  Investigation  shows  that  some  of  the 
cells  have  thick  walls  and  small  openings,  others,  thin  walls  and 
large  openings.  Most  specimens  of  wood  have  these  different 
kinds  of  cells  arranged  or  grouped  together  in  such  a way  as  to 
form  the  annular  rings  which  are  so  distinct  on  the  cross  section 
of  most  lumber  and  give  the  beautiful  watered  grain  to  longi- 
tudinal sections. 
When  the  growth  of  the  tree  begins  in  the  spring  or  at  the  be- 
ginning of  the  wet  season  in  most  tropical  countries,  there  is  a 
great  demand  for  water  in  the  crown  where  the  multitudes  of 
new  leaves  and  twigs  are  forming,  hence  a new  layer  of  large  loose 
thin-walled  cells  is  rapidly  built ; when  the  demand  for  crude 
sap  is  not  so  great,  and  when  there  is  plenty  of  digested  food  to 
supply  building  material,  the  cells  formed  are  narrow  and  thick 
walled ; thus  the  latter  growth  of  each  season  is  heavier,  stronger 
and  darker  in  color  than  the  earlier  growth.  As  long  as  the  tree 
is  in  good  condition,  distinct  rings  are  left,  one  for  each  year, 
which  the  foresters  and  lumbermen  make  use  of  in  determining 
the  age  of  the  trees  of  the  forest.  Fire  or  insects  or  anything  of 
the  kind  damaging  one  side  of  the  tree  will  often  be  the  cause  of 
incomplete  annular  rings.  Seasons  of  drought  leave  narrow  and 
indistinct  rings  that  prove  correct  records  of  those  dry  years 
throughout  the  existence  of  the  tree.  These  accurate  records 
were  very  valuable  to  the  parties  who  determined  the  great  ages 
of  the  grand  Sequoias  of  California. 
Other  markings,  peculiar  and  interesting,  and  that  have  much 
to  do  with  the  finishing  of  some  species  of  wood,  are  the  dappels 
or  thin  plates  of  cells  belonging  to  the  Medullary  rays.  These 
lines  of  cells  run  from  the  pith  in  the  center  to  the  bark  as  longi- 
tudinal layers.  Their  function  is  to  strengthen  and  bind  the 
annual  layers.  Though  they  are  present  in  most  tree  stems,  they 
seldom  appear  more  than  faint  lines  radiating  from  the  center  of 
cross  sections.  In  oak  they  are  very  conspicuous  and  add  great 
value  to  it.  To  get  oak  boards  well  marked  with  these  medullary 
rays,  the  logs  are  cut  into  quarters,  each  quarter  being  ripped 
up  into  boards  with  their  cutting  plane  oblique  to  the  quartering 
