FORMATION  OF  GUM  TRAGACANTH. 
163 
made  in  Greece  by  Eraas  (Synopsis  Plant.  Florece  Olassicce,  p. 
59),  who  states  that  no  gum  is  produced  in  the  mountains  of 
the  Peloponnesus  by  Astragalus  artistatus  and  A.  ereticus,  nor 
on  Mount  Parnassus,  nor  on  the  drier  mountains  generally,  whilst 
there  is  gum  collected  in  Achaia.  He  considers  the  exudation 
of  the  gum  as  dependent  upon  climate  influences,  and  ascribes  it 
to  the  quantity  of  cold  rain  alternating  with  great  heat  in  the 
mountains  of  Oalaryta,  &e. 
Labillardiere,  from  the  facts  observed  by  him,  draws  the  con- 
clusion that  the  tragacanth  shrub,  exposed  during  the  day  to  the 
broiling  heat  of  the  sun,  partakes  quickly  of  the  moisture  of 
fogs,  and  that  the  gum  tragacanth,  swollen  by  the  moisture  of 
fogs  and  dews,  forces  a  passage  through  the  pores  of  the  bark, 
and  appears  in  the  form  of  twisted  worms  or  drops. 
The  observations  of  Labillardiere  induced  De  Candolle  (As- 
tragologia,  1802,  p.  12,)  to  explain  the  manner  in  which  gum 
tragacanth  is  forced  out  in  a  somewhat  different  way.  He  com- 
pared the  exudation  of  tragacanth  with  that  of  the  Nemaspora 
erocea  (at  that  time  held  to  be  a  mere  gum,  and  not  a  plant), 
from  the  bark  of  beech-wood,  preserved  in  a  moist  place.  This 
view  he  still  maintained  in  his  Physiology  (L,  p.  175,)  after 
he  had  acknowledged  JSFemaspora  to  be  an  independent  plant, 
having  been  convinced  that  the  appearance  of  Nemaspora  on 
dead  trees  stood  in  connexion  with  the  moisture  of  the  atmos- 
phere, and  concluding  from  this  fact  that  the  influence  of  mois- 
ture caused  the  wood  to  expand  more  than  the  bark,  in  conse- 
quence of  which  the  former  was  as  if  tightly  sheathed,  and 
therefore  could  press  mucilaginous  substances  contained  in  the 
inner  layers  of  the  bark  to  the  surface.  This  explanation  did 
not  meet  with  favor  from  Treviranus  (Physiol,  ii.,  p.  21,)  who 
assumed  that  the  appearance  of  the  gum  originated  in  an  in- 
creased secretion  of  the  same. 
The  above-named  botanists  entertained  not  the  slightest  doubt 
that  gum  tragacanth  was  a  mucilaginous  sap  secreted  by  the 
plant ;  and  the  same  applies  to  the  pharmacologists,  even  the 
most  recent,  as  for  instance,  Pereira.  Kutzing  (Philosoph.  Bot- 
anik,  i.,  p.  203,)  on  the  contrary,  in  consequence  of  microscopi- 
cal investigations  of  the  exuded  gum,  advanced  the  view  that  it 
was  an  independent  organism,  a  fungus,  consisting  of  cells  filled 
