176  The  Apocynacece  in  Materia  Medica.  {^mS;^01- 
this  is  not  appreciable  and  the  true  caoutchoucs  of  Africa  are  furn- 
ished by  these  Apocynaceae.  The  Vahea  tomentosa  Leprieur, 
furnishes  a  large  proportion  of  the  Senegal  caoutchouc.  The  V. 
Senegalensis  A.  DC.  likewise  is  said  to  yield  a  large  quantity. 
These  lianes  are  of  small  diameter  and  greatly  entangled  and  the 
most  usual  method  of  collection  is  to  cut  them  and  collect  the  juice, 
which  flows  very  rapidly.  Each  plant  yields  3  to  4  kilos  of  caout- 
chouc. The  solidification  is  accomplished  by  water  containing  acids 
or  salt  in  solution.  In  the  interior  of  the  continent,  the  coagulation 
seems  to  be  accomplished  by  sun  heat  and  the  product  made  into 
balls  with  ashes.  This  caoutchouc  enters  commerce  generally  in 
plates  weighing  130  to  150  gm.  blackish  externally,  and  grayish 
within  and  containing  a  large  proportion  of  water,  or  in  balls,  more 
highly  esteemed  and  freer  from  impurities,  varying  from  8  to  60  gm. 
and  united  in  groups  of  from  15  to  20,  and  these  are  of  a  rose 
color. 
The  Landolfia  Heudelotii  A.  DC.  and  the  L.  Owariensis  Pal.  de 
Beauv.,  are  important  as  caoutchouc  producing  plants.  They  inhabit 
the  western  side  of  tropical  Africa  and  the  latter  plant  is  said  espe- 
cially to  produce  the  caoutchouc  from  Sierra-Leone,  which  appears  in 
balls,  mostly  of  a  slate  color  internally.  The  Landolfia  flortda  Benth, 
occupies  an  altitude  of  2,500  feet  and  is  found  also  in  Mozambique 
and  is  the  source  of  a  large  amount  of  caoutchouc.  The  caoutchouc 
of  Gaboon  is  undoubtedly  derived  from  the  two  last-named  plants. 
It  appears  in  masses,  white  upon  cutting,  quite  consistent,  contain- 
ing much  waterand  but  little  foreign  matters.  It  is  readily  purified 
and  then  remains  firm  and  resistant.  It  is  estimated  that  from  the 
French  colonies  there  is  annually  exported  400  tons.  The  Lan- 
dolfia Kirkii  occupies  the  oriental  regions  of  Africa,  especially  Zan- 
zibar and  Mozambique,  being  the  "  Matire "  or  "  Mtiri "  of  the 
natives.  It  is  the  most  important  species  of  this  region  and  its 
latex  solidifies  spontaneously  so  readily  that  artificial  coagulation  is 
unnecessary.  The  exportation  of  this  product  in  1879  Was  valued 
at  1,125,000  francs.  The  L.  Petersiana  inhabiting  the  same  region 
is  characterized  by  an  extremely  fluid  latex,  the  coagulation  being 
secured  by  acids  or  by  fire. 
The  caoutchoucs  of  Madagascar  are  furnished  by  Vahea  mada- 
gascariensis  Boj.  V.  gnmmifera  Lamk,  and  V.  Comore?isis  Boj.; 
and  are  coagulated  by  acids,  lemon  juice  being  mostly  used. 
