ON  THE  PURGATIVE  CONVOLVULACEiE. 
207 
Several  facts  are  presented  of  a  novel  character,  that  were 
derived  from  M.  Boucard,  a  young  naturalist,  who  spent  several 
consecutive  years  in  Mexico. 
It  was  known  that  jalap  grew  spontaneously  in  the  environs  of 
Xalapa,  and  in  the  principal  Sierra  within  a  certain  zone  of  its 
altitude,  varying  from  1,500  to  2,000  metres  above  the  level  of 
the  sea ;  but  what  was  previously  unknown  is  that  this  altitude 
is  necessary  to  the  vegetation  and  complete  development  of  true 
jalap.  They  have  sought  to  acclimate  it  to  the  lower  height  of 
the  plateau  of  Xalapa,  and  have  planted  it  particularly  at 
Huatusco ;  but  these  attempts  have  not  given  satisfactory 
results. 
According  to  the  observations  of  M.M.  Boucard  and  Mendez, 
jalap  grows  by  preference  in  the  mountains,  in  cool  and  moist 
pjaces.  The  most  beautiful  individuals  were  encountered  in  a 
porous  light  soil,  shaded  by  a  forest  of  pines  and  oaks;  and 
whenever  a  place  of  suitable  altitude  occurs  where  a  torrent 
descends,  jalap  is  certain  to  be  found  on  its  borders,  sheltered 
from  the  sun. 
Besides  the  two  jalaps  which  have  been  noticed  here  and  are 
in  commerce,  M.  Andouard  has  observed  a  third  sort,  called 
Tampico,  but  in  truth  of  unknown  origin.  To  these  three 
sorts,  it  is  necessary  to  add  a  fourth,  recently  introduced  into 
France,  and  which  M.  Guibourt  has  provisionally  called  digitate. 
These  different  species  of  jalap  are  very  far  from  having  the 
same  value,  that  is  to  say,  the  same  content  of  resin.  In  taking 
tuberous  or  officinal  jalap  of  good  quality  as  a  type,  we  find  it 
contains  from  16  to  17  per  cent,  of  resin,  and  that  male  jalap  of 
Ledanois,  or  fusiform  jalap  contains  from  9  to  10  per  cent., 
according  to  Ledanois  himself,  following  our  best  authors,  and 
according  to  the  repeated  and  varied  essays  of  the  Commission. 
M.  Andouard,  on  his  side,  alleges  the  proportions  of  from  14  to 
20  per  cent. — more  than  in  the  tuberous  jalap — whence  he 
believes  that  he  is  able  to  conclude  that  the  therapeutic  value 
of  these  two  jalaps,  tuberous  and  fusiform,  is  at  least  equal. 
M.  Marais  regards  this  affirmation  as  premature  after  he 
examines  the  results  of  other  experimenters,  and  considers  it 
dangerous,  because  it  furnishes  a  pretext  for  substitutions  and 
