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PLANTS 



walled spherical or polygonal cells. Such tissue is generally 

 termed parenchyma. In this case it occupies the axis of the 

 stem and forms the pith. There are also radial extensions 

 of the parenchyma from the pith toward the surface of the stem. 

 The disposition of the parenchyma in a cross section might 



Parenchyma 



Fig. io. — Cross section of a typical dicotyledon stem from the pith to the 

 epidermis and comprising one vascular bundle. See preceding figure. 



therefore be likened to the hub and spokes of a wheel. In 

 the position corresponding to the felloes of the wheel there is 

 also more or less parenchyma. 



73. The tire of the wheel is represented by a single layer 

 of brick-shaped cells whose outer walls are thickened and form 



