190 THE ELEMENTS OF VEGETABLE HISTOLOGY 



materials the fibers and vessels are usually clearly 

 apparent. The fibers occur in groups, are thin-walled 

 and comparatively few in number. The vessels occur 

 either separately or in conjunction with the fiber masses. 

 Spiral or annular vessels are the predominating types. 

 In powdered leaves these elements are apparent on 

 longitudinal view. 



CELL CONTENTS 



The cell contents of leaves are stored within the 

 palisade cells, mesophyll parenchyma, secretion cells 

 and glandular hairs, and occasionally in the fibers. 

 The most important stored material is chlorophyll, 

 a protoplasmic cell content. The nonprotoplasmic 

 contents include volatile oils, calcium oxalate crystals 

 and calcium carbonate deposits or cystoliths. 



FUNCTIONS OF LEAF TISSUES 



The functions of the different structures present 

 in leaves may be tabulated as follows: 



/-.-, ( Epidermis, 



Covering tissues < _*_. . 



I Inchomes. 



Bast fibers (traces), 



Supporting tissues. . . \ ? a ^ ers (traces) ' 

 Collenchyma, 



Stone cells (rarely). 

 Sieve tubes, 



Conducting tissues. 



Vessel sheaths, 

 Mesophyll. 

 Absorbing tissues Stomata. 



Ducts, 



Assimilating and 

 synthesis tissues . 



Palisade, 

 Mesophyll, 

 Secretion cells, 

 Glandular hairs. 



Storage tissues. . . / Secretion cells, 



I Glandular hairs. 



