J75 
Alba. — Castilloa  elastica  alba  produces  a thick  creamy  milk.  It 
is  the  hardiest  of  all  Castilloa  trees,  and  suffers  very  little  from  the 
tappincT  operation.  It  also  yields  the  largest  quantity  of  rubber. 
The  bark  of  this  variety  is  white,  with  a distinct  yellowish  or 
piqkish  cast. 
Negra. — Castilloa  elastica  negra  is  characterised  by  a very  rough 
dark  bark.  It  yields  very  readily  a thin  milk  producing  a good 
rubber,  but  the  tree  in  tapping  easily  bleeds  to- death. 
Rubra. — Castilloa  elastica  rubra  has  a reddish  bark  which  is 
very  smooth,  thin,  and  brittle ; nor  does  it  show  the  longitudinal 
furrows'  which  are  noticeable  in  the  two  hrst-aamed  trees.  This 
variety  yields  a very  small  quantity  of  milk,  but  the  rubber  obtained, 
from  it  is  good.  The  tree  is  very  common  all  over  Central  America, 
and  I am  afraid  that  in  a number  of  instances  it  was  this  tree  which 
was  planted  instead  of  the  white  Castilloa.  Indeed,  Koschny  is 
inclined  to  think  that  it  is  this  variety  with  which  the  experiments 
in  the  Botanical  Gardens  in  Ceylon  and  Java  were  made  which  gave 
such  discouraging  results. 
Shade  or.  Open. — The  question  whether  Castilloa  should  be 
planted  in  the  shade,  or  in  open  land  has  been  answered  both  ways. 
It  is  possible  that  the  climatic  conditions  of  the  district  in  which 
the  plantation  is  situated  may  have  some  influence  upon  this  point. 
However,  all  the  reliable  evidence  seems  to  show  that  the  trees 
grow  badly  in  dense  forests,  and  produce  a poor  yield  of  rubber 
when  grown  on  open  ground.  They  appear  to  prosper  best  when 
growing  up  together  with  other  trees,  so  that  the  trunk  is  always 
shaded,  whilst  the  top  of  the  tree  at  least,  for  a certain  time  during 
the  day,  receives  the  direct  rays  of  the  sun,  from  what  I have 
seen  at  Las  Cascadas  I entertain  no  doubt  whatever  the  last 
named  condition  is  the  most  favourable  for  the  growth  of  the  trees. 
Clearing. — This  being  admitted,  it  is  obvious  that  in  planting 
Castilloa  in  open  land  it  is  necessary  to  plant  at  the  same  time  trees 
to  protect  and  partly  shade  it.  As  this  adds  very  greatly  to  the 
co.st  of  planting,  it  stands  to  reason  that  in  selecting  land  for  the 
cultivation  of  Castilloa,  preference  should  be  given  to  forest  land. 
The  larger  trees  are  cut  out — there  are  generally  plenty  of  uses  for 
them  on  the  plantation — only  the  smaller  trees  being  left  standing 
between  which  the  rubber  trees  are  planted. 
Soil. — As  regards  the  configuration  of  the  land,  and  the  best 
quality  of  the  soil,  some  little  discrimination  is  also  required. 
Regarding  the  soil,  it  may  be  said  that  Castilloa  is  very  modest 
indeed,  but,  of  course,  this  does  not  mean  that  just  any  soil  is  good 
enough.  The  best  results  are  undoubtedly  obtained  on  a deep, 
loamy,  only  moderately  .sandy  soil.  Whether  Castilloa  should  be 
planted  on  level  or  on  hanging  ground  is  a rather  more  important 
question.  In  Mexico,  I believe,  rather  large  level  tracts  have  been 
planted,  but  then  the  rainfall  in  Mexico  Is  considerably  less  than 
what  it  is  in  Colombia.  It  is  quite  certain  that  the  trees  require 
well-drained  land,  and  this  with  a rainfall  of  130  Inches,  the  figure 
for  the  Isthmus,  means  hanging  land.  There  are  Immense  traces 
