202 



PLANT ORGANS OR PARTS OF PLANTS. 



tissue undergoes corky modification which results in the 

 brown nodules which break through the epidermis, 

 forming the spots found on the surface of the leaf. The 

 mesophyll, through which nm the fibro- vascular bundles, 

 constituting the nerves, consists of somewhat irregular, 

 but far more compact, tissue than is the rule. The cells, 

 as well as those of the palisade layers, contain many 

 crystals of calcium oxalate, both single and in glomerules. 

 The nerves, which are compact and well developed, 



Fig. 54. — Eucalyptus. 

 Cross-section of leaf of eucalyptus showing large schizogenous oil 

 cell in the m, mesophyll; p, parenchyma filled with chlorophyll, pali- 

 sade cell arrangement; sp, stomata; K, crystals (Moeller). 



consist of wood bundles arranged in regular rows, sur- 

 rounded by bast fibres which are somewhat thickened 

 on the periphery. The whole bundle is surrounded by a 

 ring of woody parenchyma, which on each side becomes 

 collenchymatic and extends to the epidermis of upper and 

 lower surfaces. 



