Stem and Root Structures 



77 



each bundle is surrounded by a fibrous sheath developed from 

 the ground tissue. 



FIG. 74. Part of a transverse section through the stem of Tradescantia 

 Sello'i : o, epidermis, with a sioma, sp ; R, cortex ; V, thickening ring with the 

 outer vascular bundles, g 1 ; g" , inner vascular bundles ( x 75). 



Secondary Thickening in Monocotyledons. Since 

 the closed bundles of monocotyledons allow for no secondary 

 thickening, the structure of the mature stem resembles that of 



