36o  '         Histology  of  Araroba,  { "^""ji^y'is^so^™" 
tive  influences.  The  granular  protuberances  seen  in  a  section  of  the 
bark  are  due  to  these  sclerogen  cells  being  left  intact,  whilst  those  con- 
taining the  starch  grains  have  to  some  extent  given  way. 
No.  I— Segment  of  Araroba.  2— Transverse  section  of  Araroba, 
enlarged, — <2,  meduHary  rays;  por- 
ous vessels  j  r,  parenchyma  of  wood  j 
libriform  cells. 
With  reference  to  the  bark  little  need  be  said,  as  it  does  not  appear 
to  enter  into  the  composition  of  araroba.  Within  the  bark  is  the 
woody  column,  traversed  from  the  medulla  to  the  bark  by  narrow 
medullary  rays  colored  by  the  araroba,  and  the  round  spots  show  the 
porous  vessels,  most  of  them  also  filled  with  the  same  substance. 
The  drawing  No.  2  shows  a  small  part  only  of  the  woody  column 
of  this  segment,  enlarged  as  seen  under  the  microscope,  and  bounded 
on  either  side  by  the  medullary  rays.  The  whole  segment  of  No.  I 
being  only  a  repetition  of  this  section,  an  explanation,  therefore,  of  the 
cellular  structure  of  this  portion  will  give  the  cells  comprising  the 
whole.  It  exhibits  four  distinct  forms  of  cells.  There  are  the  medul- 
lary rays,  ^,  on  either  side  ;  they  are  usually  two  cells  wide,  narrow, 
thin-walled  and  elongated  in  a  radial  direction,    h  represents  porous 
