CHAPTER XV 

 LEAF STRUCTURE 



The leaves are lateral extensions of the stem, 

 which have been expanded or otherwise modified in 

 structure to function as manufacturing and assimilating 

 organs. In their histological characters, leaves show 

 many of the elements characteristic of primary stem 

 structure; and, although these elements are more or 

 less modified, a direct relationship can be traced 

 between them and the cortex and central cylinder 

 of the stem. Leaves manufacture the greater portion 

 of the starch and may take part in the manufacture 

 of other plant nutrients. These nutrient materials 

 are transported through the leaf stem or petiole, and 

 thence through the vascular tissues of the stem, to 

 plant organs requiring nutrients or to storage tissues. 

 The tissues present in leaves, in the order of their 

 arrangement are as follows : 



1. Upper epidermis, 



2. Upper palisade, 



3. Leaf parenchyma or mesophyll, 



4. Fibro-vascular elements, 



5. Lower palisade, 



6. Lower epidermis. 



CHARACTERS OP THE LEAF TISSUES 



Epidermis. — The leaf epidermis usually consists 

 of a single layer of strongly cutinized cells which 

 function as a transparent, protective tissue. On 



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