Fig.  4,  transverse  section  of  the  mid-rib  of  a  leaf  of  Solanum  Carolinense, 
with  one  of  the  prickles,  which  is  shown  in  longitudinal  section,  attached  ; 
magnification,  150  diameters.  A,  epidermal  cells  ;  b,  parenchyma  of  upper 
portion  of  mid-rib  ;  c,  a  portion  of  the  lamina  of  the  leaf ;  d,  xylem  tissue  of 
mid-rib ;  e,  cambium  zone  ;  f>  phloem  tissue  of  mid-rib  ;  g,  parenchyma  of 
lower  portion  of  mid-rib  ;  k,  collenchyma  tissue  ;  if  slightly  lignified  tissue  of 
the  prickle,  which  occurred  on  the  mid-rib  and  was  cut  through  longitudinally; 
ky  epidermal  tissue,  more  lignified. 
