ROOT HISTOLOGY 



17 



2. Biennial plants develop but one set of organs the first year, and 

 as in the beet and turnip, etc., a large amount of reserve food material 

 is stored in the root for the support of the plant the following season 

 when it flowers, fruits, and dies. 



3. Perennial plants live indefinitely, as trees. 



Root Histology. Monocotyledons. — The histology of mono- 

 cotyledonous roots varies, depending upon relations to their surround- 

 ings, which may be aquatic semi-aquatic, mesophytic, or xerophytic. 



Fig. 13. — Sarsaparilla, Mexican. Cross-section of root. (32 diam.) A, Root 

 hairs; B, cork; C, parenchyma of cortex; Z), endodermis; £, wood parenchyma 

 and fibers; F, water tube; E, phloem. (Photomicrograph.) {From Sayre.) 



In this connection we will discuss only the type of greatest pharma- 

 cognic importance, i.e., the mesophytic type as seen in its most typical 

 form in the transverse section of an Onion root. 



Examiniag such a section from periphery toward the centre, one 

 notes the following : 



1 . Epidermis with thin cuticle. 



2. Cortex, consisting of broad zone of rounded cells getting larger 



