AjanuarryXm'}        The  Anatomy  of  Edible  Berries,  27 
diameter,  and  cell  walls  about  0-003  millimeter  thick.  Cross-sec- 
tions show  that  this  layer  is  about  O  O25  millimeter  thick  and  that 
the  cuticle  is  strongly  thickened. 
(2)  The  Hypoderm  {Fig.  28)  is  for  the  most  part  only  one  cell- 
layer  thick,  and  the  cells  are  more  or  less  isodiametric  in  cross-section. 
Evaporation  is  largely  prevented  by  the  thick  cuticle,  rendering  a 
more  strongly  developed  hypoderm  unnecessary. 
(3)  The  Mesocarp  cells  are  mostly  isodiametric,  and  range  up  to 
0-20  millimeter  in  diameter,  but  in  the  partitions  of  the  fruit  cavities 
they  are  somewhat  smaller. 
(4)  The  Endocarp  {Fig.  20)  is  from  0-02  to  0-05  millimeter  thick 
and  is  made  up  of  a  single  layer  of  cells.  As  is  seen  in  surface 
preparations,  the  cells  are  for  the  most  part  longitudinally  extended 
and  are  more  or  less  curved  or  wavy  in  outline.  The  indistinctly 
porous  cell  walls  are  somewhat  thicker  than  those  of  the  mesocarp, 
but  unlike  those  in  some  Vaccinium  species  are  not  conspicuously 
Fig.  32. — Mountain  Cranberry  (  Vaccinium  Vitis-Idaed).  Transverse  section 
of  testa.    X  160. 
sclerenchymatized.  Although  stomata  are  entirely  lacking  in  the 
epicarp,  it  is  a  remarkable  fact  that  they  occur  in  considerable  num- 
bers in  the  endocarp. 
Testa. — (1)  Epidermis  (Fig.  30,  ep,  Fig.  jr). — Of  all  the  tissues 
of  the  cranberry,  this  layer  is  the  most  characteristic  and  remark- 
able. The  cells  in  the  mature  seed  range  in  width  up  to  O-i  milli- 
meter and  in  length  up  to  0-4  millimeter,  but  in  abortive  seeds  are 
much  smaller.  As  is  seen  in  cross  section,  the  outer  walls  (Fig. 
30,  ep)  are  thin  and  convex,  but  the  deep  yellow  or  brown  inner 
and  radial  walls  are  sclerenchymatously  thickened  (double  radial 
walls  often  0  02  millimeter  thick),  and  in  addition  the  radial  walls 
and  sometimes  the  outer  and  inner  walls  have  a  transparent  muci- 
laginous layer  of  distinctly  stratified  structure  which  nearly  fills  the 
cell  cavity.  Treated  with  zinc-chloride-iodine  the  mucilaginous 
formation  is  stained  blue,  the  cell  walls  proper  remaining  yellow. 
In  V.  Vitis-Idaea  the  outer  and  inner  walls  often  have  a  swollen 
