BIOLOGY OF HIGHER SEED PLANTS 53 



B. STRUCTURE OF ROOTS 



Study transverse sections of large and small roots and com- 

 pare their structure with that of herbaceous and woody stems 

 of dicotyledons. 



1. Bark. Do roots possess a definite bark ? Has the bark 



(including tissues between epidermis and cambium) the 

 same general layers as in stems ? Are these layers simi- 

 lar in arrangement and structure in stems and roots ? 



2. Xylem and pith. Are these two regions the same in roots 



and stems ? Compare young and old roots in this respect. 



a. Dead tissues of the xylem. Do you find ducts and 



fibrous cells ? How are they arranged in roots ? Are 

 there annual rings ? 



b. Living tissues of roots. Are these more or less abundant 



in roots than in stems? Stain fresh root sections 

 with iodine to demonstrate this point. 



3. Cambium and phloem. Are these tissue layers present 



in the root section that you are studying ? Are they 

 as evident as in stem sections ? 



4. Drawing. Construct a drawing of a root in transverse 



section (no cells), to illustrate root structure. Label the 

 tissue layers correctly. 



5. Summary. Summarize the distinctive features of root 



structure as compared with that of herbaceous stems. 



C. THE STRUCTURE OF THE LEAF 



For the preliminary study of the structure of a leaf use thick 

 leaves of Narcissus or onion, which are easily sectioned in a 

 fresh state. 



1. Epidermis. Peel or strip the epidermis from a leaf of the 

 onion or Narcissus. Mount in water or dilute alcohol 

 and study its cellular structure. 



