THE CHLOEOPHYLL APPAEATUS 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 



s.pa 



Fio. 86. TRANSVERSE SECTION OP PORTION OP THE BLADE OP THE 

 LEAP OP Beta. 



cu, cuticle ; ep, epidermis ; p.pa, palisade tissue ; s. pa. spongy tissue ; 

 v.b, vascular bundle ; st, stoma ; i.a, 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 



