CHAPTER XIII 

 ROOT STRUCTURES 



IN considering the histology of roots it is noted that 

 the roots of many classes of plants undergo the changes 

 noted in Chapter VI, resulting in the development 

 of secondary or permanent tissues. Other types of 

 roots do not undergo this series of changes incidental 

 to the production of secondary structures. There- 

 fore it is convenient to subdivide root structures into 

 those found in secondary roots and those present in 

 primary roots. The roots of most monocotyledons 

 retain their primary structures throughout the life 

 of the plant. Dicotyledonous roots, while exhibiting 

 primary structures during the earlier stages of growth 

 soon undergo modification resulting in the formation 

 of secondary structures. The chief differences between 

 the primary and secondary types of roots are in the 

 nature of the covering tissues, the arrangement of 

 the fibre-vascular bundles, and the presence or absence 

 of a distinct endodermal layer. 



PRIMARY ROOT STRUCTURES 



Primary root structures are present in the earlier 

 stages of root development of both monocotyledons 

 and dicotyledons; but, in the former class of plants, 

 primary structures are retained throughout the life 

 of the individual. The tissues usually present in roots 



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