THE CHLOROPHYLL APPARATUS 151 
well as those of the mesophyll. In the higher plants they 
are found most prominently in the mesophyll of the 
leaves, the epidermis as a rule being free from them. 
When the leaves are dorsiventral in structure, the 
Fia. 86.—Transverse Section or Portion oF THE BLADE OF THE 
Lear or Beta. 
cu, cuticle; ep, epidermis; pa, palisade tissue; s.pa, spongy tissue ; 
v.b, vascular bundle; st, stoma; i.s, intercellular space, 
chloroplasts are more numerous in the palisade paren- 
chyma which lies just below the upper epidermis than they 
are in the spongy tissue which occupies the lower half of 
the thickness of the leaf (fig. 86). The guard-cells of the 
stomata, however, always contain them. The green cortex 
of young stems and twigs also exhibits them. In such 
