^mAJugU!-i?7h6.rm'}        The  International  Exposition.  373 
ground  becoming  moist  from  rain,  and  the  temperature  of  the  air  lower,  the  supply 
of  oil  falls  off. 
The  mallee  scrub  is  the  opposite  of  all  this.  These  dwarfs  of  the  eucalypts 
seldom  grow  higher  than  25  feet,  and  occupy  a  flat,  dry,  hungry  country,  with  but 
little  growth  of  grass  under  them,  chiefly  dwarf  heath  bushes.  There  is  little 
Tain,  but  when  it  comes  it  is  generally  in  torrents  5  the  soil  is  a  reddish  sand,  in 
combination  with  salt  clay  ;  this,  during  the  long  droughts,  becomes  exceedingly 
hard,  so  much  so  that  a  pickaxe  is  required  to  turn  the  soil.  The  rootlets  run 
somewhat  in  a  horizontal  direction,  but  the  rootlets  spread  traveling  downward  ; 
and,  as  the  salt  water  is  to  be  obtained  always  at  from  25  to  40  feet,  they  are  found 
resting  on  the  moisture  of  the  salt  soil,  just  above  the  sandstone  rock,  which 
generally  commences  about  12  feet  above  the  salt  spring.  The  temperature  of  the 
surface  ground,  and  also  that  of  the  air,  is  very  high  throughout  the  summer. 
The  leaves  supply  a  greater  amount  of  oil  during  the  winter  or  rainy  months  than 
during  the  hot  summer  months. 
These  circumstances  depend  partly  upon  the  development  of  new  leaves,  which 
in  the  desert  species  commences  in  summer  (December  and  January),  but  in  the 
amygdal'ina.)  globulus  and  others  in  winter  (July  and  August).  Moreover,  the 
vigor  of  the  eucalypts  is  greater  in  some  years  than  others,  and  when  little 
new  growth  takes  place  the  oil-cells  are  charged  more  equally  throughout  the 
whole  year. 
To  illustrate  further:  In  July,  1872,  the  ground  being  well  saturated  with 
moisture,  the  mallee  was  in  fine  oil  condition,  each  two  tons  of  rough-cut  branches 
with  their  leaves  gave  two  (Imperial)  gallons  of  oil.  The  dry  season  set  in  imme- 
diately after,  the  temperature  of  the  air  rose  rapidly  to  summer  heat,  ranging 
between  68  and  92°  F.,  and  in  November  the  country  was  greatly  parched  and  the 
only  water  obtainable  was  from  the  river  Murray.  The  yield  of  oil  decreased  in 
November  to  14  pints,  in  the  beginning  of  December  to  12,  by  the  end  of  the  year 
to  9  pints,  and  by  the  end  of  summer  (March)  fluctuated  between  8  and  4  pints. 
During  the  same  winter  (July),  the  amygdalina  yielded  only  one-fifth  of  its  full 
summer  supply.  The  variations  during  the  two  preceding  years  were  similar, 
but  not  as  rapid,  while  in  1861  the  mallee  yielded  as  much  volatile  oil  in  December 
as  in  July  1872,  and  the  coast  species  kept  up  a  good  supply,  with  little  change, 
throughout  the  whole  year. 
The  volatile  acid  is  contained  more  abundantly  in  those  eucalypts  which  yield 
medium  quantities  of  oil  than  in  those  yielding  oils  either  largely  or  sparingly.  In 
like  manner  this  applies  to  the  resin  bodies.  In  the  amygdalina,  when  the  gum- 
resin  begins  to  form  and  exude,  the  oil  in  the  leaves  is  diminished.  When  the 
globulus  is  extra  resiniferous,  the  acid  is  abundant  and  the  oil  small  in  quantity. 
The  rostrata  produces  little  oil,  but  the  volatile  acid  is  very  abundant,  so  that  the 
red  gum  wood  owes  its  aroma  entirely  to  this  acid.  The  sideroxylon  supplies  oil 
abundantly,  but  the  leaf  surface  is  small  in  comparison  with  other  species,  and  the 
enormous  bark  is  everywhere  studded  with  gum  resin. 
All  these  characteristics  point  to  the  conclusion  that  the  volitile  oil  is  the  base  of 
the  other  eucalyptic  products. 
