AFebr0uaryffl)7m'}     The  Internal  Structure  of  the  Stem  and  Leaf.  55 
many  short  hairs  [Figs.  5  and  6)  along  the  margins  and  along  the 
veins,  on  the  dorsal  face  especially.  Viewed  "  en  face  "  the  lateral 
cell-walls  of  epidermis  are  undulate  on  both  sides  of  the  leaf,  but 
the  undulations  are  not  so  pronounced  as  in  Ruellia  and  Phlox 
subsidiary  where  epidermis  covers  the  midvein  the  lateral  walls  are 
very  thick  and  porous  {Fig.  5).  The  stomata  {Fig.  p)  occur  only  on 
the  lower  face ;  they  have  no  subsidiary  cells,  and  are  mostly  sur- 
rounded by  three  ordinary  epidermis-cells. 
The  chlorenchyma  {Fig.  j)  shows  one  stratum  of  typical  palisades 
{P)  and  an  open  pneumatic  tissue  of  three  layers.  Above  and  be- 
low the  stronger  lateral  ribs  and  the  mediane  are  strata  of  hypo- 
dermal  collenchyma  and  of  thin-walled  water-storage  tissue,  which 
reaches  its  highest  development  in  the  midrib,  and  on  the  dorsal 
face  of  this.  The  mestome-strands  are  collateral  and  quite  broad  ; 
they  all  possess  closed  parenchyma-sheaths.  While  no  crystals 
were  observable  in  Phlox,  we  find  in  the  leaf  of  Spigelia  small 
needle-shaped  crystals  of  calcium  oxalate  in  the  colorless  paren- 
chyma that  surrounds  the  veins. 
Considered  by  themselves  the  leaves  of  our  plants  do  possess  a 
very  distinct  structure,  by  which  they  may  be  readily  distinguished. 
Although  they  are  bifacial  in  regard  to  the  distribution  of  stomata 
as  well  as  to  the  differentiation  of  the  chlorenchyma,  some  charac- 
teristics may  be  pointed  out  so  as  to  separate  them  from  each  other. 
For  instance,  the  occurrence  again  of  cystolithes  in  Ruellia,  and  the 
small  glandular  hairs  observed  in  this  genus  (Fig.  11) ;  furthermore, 
the  presence  of  subsidiary  cells  in  Ruellia,  and  their  absence  from 
the  two  other  plants.  The  total  lack  of  crystals  in  Phlox  in  contrast 
to  Ruellia  and  Spigelia;  furthermore,  the  cuticular  striations  are 
very  characteristic  of  the  species  of  Phlox.  Glandular  hairs  like 
those  observed  in  Ruellia  and  Phlox  seem  to  be  absent  from  Spigeliay 
while  the  short,  more  or  less  obtuse  hairs  {Figs.  5  and  6)  are  charac- 
teristic of  this  genus. 
We  might  condense  the  anatomical  characterization  still  farther, 
and  state  that  Spigelia  Marilandica  L.  has  a  four-winged  stem  and 
bicollateral  mestome-strands,  characters  that  are  not  to  be  found  in 
either  Ruellia  or  Phlox. 
Brookland,  D.  C,  October,  1906. 
