February  11,  1897. 
JOURNAL  OF  HORTICULTURE  AND  COTTAGE  GARDENER. 
Ill 
HOW  -TREES  ARE  BUILT. 
It  is  generally  known  that  the  cone  is  the  strongest  structure  in 
Nature.  Trees  may  be  regarded  as  arborescent  cones,  for  if  we 
examine  the  stem  and  br  inches  of  them  when  denuded  of  the 
leaves  we  perceive  at  once  that  they  are  so  constructed.  The  main 
stem  is  broadest  at  its  base,  and  decreases  gradually  towards  the 
ends  ot  the  branches.  A  branch  in  the  side  place,  where  a  side 
branch  starts  from,  is  thicker  than  the  side  branch,  and  this  in  turn 
ia  thicker  than  the  branchlet  it  produces.  In  this  way  the  thick¬ 
ness  of  the  main  stem  steps  away,  so  to  say,  by  degrees  from 
branch  to  branch,  finally  losing  itself  almost  in  the  thin  branchlets 
of  the  latest  shoots. 
A  transverse  section  of  a  Beech  tree,  for  example,  shows  a 
number  of  concentric  and  almost  circular  beds  of  wood,  ensheath- 
ing  one  another  about  a  common  centre,  which  is  occupied  by  a 
canal  of  pith,  the  whole  being  covered  by  the  bark  on  the  outside  of 
the  stem.  A  longitudinal  section,  however,  shows  that  the  stem  is 
composed  of  a  number  of  superposed  and  hollow  elongated  cones, 
the  older  ones  forming  a  foundation  for  the  new  ones  then  forming 
and  of  succeeding  years.  The  conical  growth  results  from  the  conical 
formation  of  the  first  shoots,  and  is  the  foundation  of  the  subse¬ 
quent  annual  additions  of  wood  and  bark,  for  as  these  are  deposited 
in  strata  parallel  with  the  first  year’s  wood  and  bark  the  conical 
form  of  the  later  layers  is  necessarily  maintained.  Growth  in 
thickness  and  length  is  therefore  the  result  of  the  same  vegetative 
cause — the  formation  each  year  of  a  fresh  conical  layer,  which 
extends  from  the  bottom  to  the  top  of  the  tree.  It  is  therefore 
evident  that  between  the  dimensions  of  length  and  breadth  the 
branches  are  more  cylindrical  the  longer  they  are,  and  more 
conical  in  proportion  as  they  are  shorter. 
As  conclusive  examples  of  well-marked  conical  growth,  those 
extremely  short  shoots  termed  thorns  may  be  mentioned — the 
Blackthorn,  for  instance.  That  thorns  are  simply  abortive 
branches  is  at  once  proved  by  the  wild  Plum  tree,  for  in  this  tree, 
when  transplanted  and  cultivated,  the  thorns  soon  develop  into 
branches.  The  Willow,  on  the  contrary,  is  an  instance  where  the 
branches  tend  to  a  more  cylindrical  form.  In  consequence  of  this 
the  branches  of  it  are  longer  and  very  pendulous,  their  water-like 
curvature  being  extremely  graceful,  and  as  they  wave  backwards 
and  forwards  in  the  wind  the  tree  presents  a-  very  picturesque 
appearance.  All  the  Conifer  ae  are  naturally  conical-growing  trees, 
and  this  is  even  apparent  in  their  appearance.  The  Juniper,  Red 
Cedar,  Spruce  Firs,  Pine,  and  others,  when  seen  even  in  the 
distance,  clearly  reveal  by  their  outlines  their  conical  growth. 
This  conical  form  is  generally  the  original  form  of  all  trees  in 
their  early  life,  At  first  growth  takes  place  in  the  direction  of  the 
main  stem,  and  that  of  the  branches  is  restricted  ;  but  after  some 
years  the  stem  grows  to  its  greatest  height,  and  then  the  growth  is 
diverted  to  the  branches,  which  then  lose  their  conical  outline, 
and  spreading  out  around  form  a  dome-shaped  or  hemispherical 
top  or  crown.  This  is  particularly  observable  in  the  Horse 
Chestnut,  the  Lime,  and  the  Elm,  which  by  reason  of  this  upper 
development  impart  a  fine  appearance  to  a  park,  in  addition  to  the 
further  recommendation  of  affording  a  perfect  shade  around  their 
base.  In  the  Coniferse  this  development  does  not  take  place,  for 
the  tree  stops  at  the  first  stage,  and  therefore  ever  retains  its  cone¬ 
like  appearance.  For  this  reason,  as  also  too  that  on  account  of 
the  simple  character  of  their  leaves  and  flowers,  coniferous  trees 
are  considered  as  of  a  low  type  of  organisation. 
Trees  undoubtedly  derive  their  elaborate  formative  material 
from  their  leaves.  This  is  apparent  even  in  a  single  shoot,  the 
figure  of  which  depends  on  the  manner  in  which  the  leaves  are 
disposed  on  its  surface  :  for  as  wood  is  formed  by  the  leaves,  when 
these  are  placed  in  regular  order  over  every  part  of  the  circum¬ 
ference  of  the  shoot,  as  in  the  Beech  and  Lime,  the  shoot  is  always 
necessarily  cylindrical,  for  the  woody  matter  proceeding  from  the 
leaves  is  thus  distributed  equally  on  all  sides  ;  but  when  the  shoots 
are  opposite  or  in  pairs  placed  at  right  angles,  as  in  the  Maple,  the 
descent  of  nourishing  matter  from  them  is  necessarily  limited  to 
that  portion  of  the  stem  immediately  below,  and  consequently  the 
young  shoots  and  branches  of  such  trees  are  square.  All,  however, 
depends  upon  the  leaves.  If  the  vital  activity  of  these  latter  is  too 
weak  to  form  wood,  if  they  remain  crowded  together  at  the  top  in 
clusters,  there  is  no  increase  in  breadth.  Take  shoots  of  the  Horse 
Chestnut,  for  example.  One  shoot  may  be  conical,  the  other  cylin¬ 
drical.  The  conical  shoot  is  the  growth  of  a  year,  the  cylindrical 
perhaps  of  ten  years,  yet  they  are  both  about  of  a  size.  As  their  woody 
matter  was  derived  from  the  leaves  which  clothed  them,  it  follows 
that  in  the  case  of  the  ten-years  shoot  .very  little  was  supplied,  and 
hence  it  is  cylindrical,  not  conical,  like  the  one  year’s  growth.  It 
follows  that  the  breadth  of  the  wood  rings  annually  formed,  and 
which  we  see  in  the  transverse  section  of  the  stem,  must  also 
correspond  with  the  amount  of  entire  leaf  surface  which  is  put 
forth  into  the  atmosphere  during  the  vegetative  season. 
To  prove  this  we  need  only  select  branches  the  leaves  of  whose 
side  shoots  are  annually  put  forth  as  leaf  clusters,  and  which,  there¬ 
fore,  exhibit  but  a  minimum  of  development,  and  consequently 
exercise  the  least  possible  physiological  influence  on  the  branch, 
and  where  powerful  growths  are  suddenly  succeeded  by  growths 
greatly  retarded.  It  is  often  seen  that  the  three  inner  rings  or 
woody  layers  formed  by  the  leaves  of  the  first  three-years  growth 
are  much  broader  than  the  four  outer  rings,  the  leaf  deposits  of  the 
next  four  years. 
These  evidences  and  others  conclusively  demonstrate  that  the 
breadth  of  the  wood  rings  is  determined,  not  by  the  activity  of  the 
leaves  of  the  terminal  shoot  of  the  main  stem,  but  that  the  leaves 
FIG.  27. — IRIS  HISTRIOIDES.  ( See  page  112.) 
of  the  side  shoots,  or  of  the  whole  system  of  shoots,  co-operate. 
Therefore  the  leafage  of  each  year  forms  a  common  source  whence 
is  derived  not  only  the  nutriment  forming  the  new  layer  of  each 
branch  or  system  of  shoots,  but  of  the  main  stem — the  support  of 
all.  The  leaves  are  therefore  indubitably  the  source  of  the 
elaborately  formative  material  which  they  furnish  to  the  shoots, 
from  the  shoots  to  the  branchlets,  and  from  these  latter  to  the 
branches,  whose  ultimate  union  forms  the  main  stem  of  the  tree, 
just  as  many  little  rivulets,  with  their  tributary  streams,  furnish, 
when  united,  a  river,  and  eventually  a  sea. 
Thus  in  the  course  of  years  solid  and  enduring  vegetable 
monuments  are  reared,  nothing  but  air  and  earth,  yet  woven  by 
magic  chemistry  as  it  were  from  these  first  elements  which  outlive 
generations  of  mankind.  Nature  builds  on  the  conical  principle  to 
insure  stability,  which  is  the  inevitable  result  of  her  work. — 
Wm.  Norman  Brown. 
The  Bunvard  Centenary  Show. — We  are  pleased  to  hear,  as  a 
result  of  the  show  which  was  held  at  Maidstone  last  autumn,  that 
5  guineas  each  have  been  sent  to  the  Gardeners’  Royal  Benevolent 
Institution,  the  Royal  Gardeners’  Orphan  Fund,  and  the  Maidstone 
Church  Institute. 
