^ptembeSf'}     The  Apocynacece  in  Materia  Medica.  45 1 
with  separate  grains ;  it  is  this  that  distinguishes  the  Apocynaceae 
and  the  Asclepiadeae. 
Disk. — Between  the  two  interior  cycles  we  find  frequently  a  nectar- 
bearing  disk,  circular  or  five-lobed,  or  two  large  glands,  or  again  a 
number  of  glandules.  These  organs  are  frequently  aborted. 
Gynoecium. — Always  of  two  free  carpels,  rarely  a  little  sunken,  the 
receptacle  developing  slightly  concave,  and  the  insertion  a  small  peri- 
gynium.  The  carpels  sometimes  distinct,  at  other  times  coherent  on 
an  ovary  bilocular,  or  more  rarely  unilocular  with  parietal  placenta- 
tion.  The  distinct  carpels  often  remain  consolidated  at  the  extremity 
with  the  base  of  the  persistent  style.  The  styles  are  at  first  free, 
then  always  united  in  a  single  one,  frequently  dilated  at  the  disk, 
below  the  stigma,  often  bifid.  The  characters  of  the  stigma  are 
often  important  for  distinguishing  neighboring  families.  Ovules, 
ordinarily  numerous,  rather  rarely  two  or  one ;  semi-anatropous, 
anatropous  or  campylotropous. 
Fruit,  very  various  in  shape  and  structure,  and  permits  the  division 
of  the  family  into  tribes ;  double  follicle,  capsule,  berry,  drupe,  one 
or  two  locular.  Seeds,  ordinarily  compressed,  always  of  a  certain 
shape,  sometimes  peltate,  alated,  or  provided  at  one  or  both  extrem- 
ities with  a  tuft  of  hairs,  or  the  awn  sometimes  greatly  developed. 
Albumen,  generally  thin,  existing  nearly  everywhere ;  cartilaginous 
or  fleshy.  Embryo,  straight,  with  the  radicle  variously  directed, 
with  two  cotyledons  plane  or  folded  or  rolled  up,  often  oily. 
Anatomy. — Laticiferous  vessels. — It  is  often  in  the  liquid  which 
they  contain  that  the  active  principle  of  the  plant  is  found,  and  the 
species  in  which  the  latex  does  not  gush  forth  in  abundance  with 
the  least  wound  is  here  an  exception.  They  are  formed  primitively 
by  a  small  number  of  isolated  cells,  elongating  themselves  at  the 
same  time  that  the  appendices  of  the  plant,  multiplying  by  innu- 
merable ramifications,  but  these  are  not  partitioned  and  do  not  anas- 
tomose. These  are  the  inarticidate  laticiferous  vessels  of  Hartig. 
These  appear  already  in  the  embryo.  Chauveaud  has  shown  the 
existence  of  these  initial  cells  (4  rarely  8  or  more)  constant  in 
number  for  each  species,  and  placed  in  the  tissue  external  to  the 
central  cylinder  of  the  young  embryo,  in  the  pericycle.  Once 
developed,  the  laticiferous  vessels  present  quite  a  diversity  in  the 
organs,  in  certain  species  being  infinitely  richer  than  in  others. 
Although  their  existence  in  the  pericycle  is  quite  constant,  they 
