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A TEXTBOOK OF THEORETICAL BOTANY 



The leaves of Monocotyledons differ from those of Dicotyledons in having, 

 in general, a lower degree of differentiation in the mesophyll. The palisade 

 layer is seldom well marked and the whole of the mesophyll tissue may be 

 spongy or parenchymatous in character. The veins are parallel and each 

 vein is frequently flanked, above and below, by masses of sclerenchyma, 

 thus forming a rib across the mesophyll, and dividing it into a series of isolated 

 strips between the veins (Fig. 988). As the leaves are usually held vertically 



Stoma 



Sclerenchyma 



Protoxylem 



Bundle sheath Mesophyll Stoma Phloem 



Fig. 988. — Zea tnais. Trans\erse section of leaf. 



the two sides of the leaf tend to be similar in structure, i.e., bifacial, with 

 stomata equally numerous on both faces (Fig. 989). 



SCLERENCHYMA 



SCLERENCHYMA 



PHLOEM 



MESOPHYLL 



Fk;. 989. — Triticum vulgare. Transverse section of the leaf showing bifacial 

 structure. {After Bniner and Weaver.) 



i 



