552  Plant  Groups,  their  Constituents  and  Properties.{Am-^T;^arm' 
Resins  are  likewise  widely  distributed  throughout  the  phanero- 
gams, and  but  few  of  these  plants  appear  to  be  destitute  of  such 
compounds.  Very  frequently  they  are  associated  with  volatile  oils, 
or  with  gum,  or  with  both ;  in  the  two  last-named  cases  they 
usually  form  milky  exudations,  from  which  the  officinal  gum  resins 
are  obtained. 
Saponin  has  received  its  name  from  a  plant  of  the  caryophyllaceae, 
in  which  order  it  appears  to  be  of  frequent  occurrence;  but  it  or  an 
allied  compound  has  also  been  shown  in  the  polygalaceae,  in  the 
rosaceous  quillaia,  in  the  smilaceae  and  other  plant-groups,  while 
volatile  acrid  compounds  exist  in  many  aroideae,  in  buttercups  and 
their  immediate  relatives.  Somewhat  allied  to  the  saponins  are 
certain  powerful  poisons  of  the  liliaceae,  primulaceae  and  of  digitalis 
and  other  scrophulariaceae. 
The  aroideous  calamus  owes  its  medicinal  virtues  to  a  volatile  oil 
and  bitter  principle,  types  of  compounds  which  are  frequently  asso- 
ciated in  the  bitter-tonic  drugs.  But  others,  like  the  simarubaceae 
and  gentianaceae,  have  developed  the  bitter  principle  to  the  total  or 
almost  complete  exclusion  of  aromatic  and  astringent  compounds. 
Many  of  the  principles  referred  to  belong  to  the  class  of  gluco- 
sides,  so  called  because  upon  decomposition  under  certain  influences 
glucose  or  an  allied  carbohydrate  makes  its  appearance  as  one  pro- 
duct. A  peculiar  group  of  the  same  class  should  be  mentioned 
here,  apparently  confined  to  the  convolvulaceae,  like  jalap  and 
scammony,  which  owe  their  cathartic  action  to  so-called  resins,  in 
reality,  to  water-insoluble  anhydrides  of  water-soluble  acids,  both 
splitting  into  compounds,  one  of  which  is  sugar. 
The  bitter  taste  is  not  solely  confined  to  the  glucosides  and  so- 
called  neutral  compounds.  A  very  large  number  of  the  most 
important  class  of  alkaloids  share  with  the  former  this  property. 
It  is  now  nearly  three-quarters  of  a  century  that  the  first  alkaloid, 
morphine,  has  been  announced  as  a  basylous  organic  compound ; 
to-day  the  members  of  this  class,  both  natural  and  artificial,  are 
almost  innumerable.  Among  the  acotyledons  it  is  almost  exclu- 
sively the  class  of  fungi  which  in  its  different  groups  produces  alka- 
loids, quite  distinct,  as  a  rule,  in  composition  and  effect,  from  those 
generated  within  the  living  tissue  of  phaenogams.  Such  alkaloids 
are  in  nearly  all  cases  confined  to  a  single  species,  or  genus,  or  tribe, 
and  only  in  rare  cases  have  been  met  with  in  several  orders.  Thus, 
