· Internal structure of monocot roots shows the following tissue systems
§ Epiblema or rhizodermis
§ Cortex and
§ Stele
The Rhizodermis or Epiblema
§ Outermost layer of the root
§ Single row of parenchyma cells, no intercellular space
§ Stomata and cuticle are absent
§ Root hairs are always unicellular
§ The key function of rhizodermis is protection of the inner tissues of the root
· The Cortex
§ The cortex is made of only one type of tissue (parenchyma)
§ Has many layers of parenchyma cells with lot of intercellular spaces
§ Cortical cells are generally oval or rounded in shape; chloroplasts are absent
§ The cells are living and possess leucoplasts
§ The inner most layer of the cortex is endodermis and is composed of single layer of barrel shaped parenchymatous cells
§ The function of cortical cells is storage
§ Endodermis (innermost layer of cortex) forms a complete ring around the stele (tissues inside endodermis)
§ There is a band-like structure made of (thickened with) suberin present in the radial and transverse walls of the endodermal cells
§ The band is called Casparian strips
§ The endodermal cells opposite to the protoxylem elements, are thin-walled without Casparian strips
§ These cells are called passage cells and their function is to transport water and dissolved salts from the cortex to the xylem
§ Water cannot pass through other endodermal cells due to Casparian strips (blocking effect)
§ The main function of Casparian strips in the endodermal cells is to prevent the re-entry of water into the cortex once water enters the xylem tissue
· Vascular System (Stele)
§ Vascular tissues are in radial arrangement with many protoxylem groups
§ This arrangement of xylem is called polyarch and the xylem is in exarch condition
§ The tissue present between the xylem and the phloem, is called conjunctive tissue
· The Pith
§ The central portion
§ It consists of thin walled parenchyma cells with intercellular spaces
§ These cells are filled with abundant starch grains
References Evans, W. C. (2009). Trease and Evans Pharmacognosy. India: Reed Elsevier Limited
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