Exercise 8: The Root

• Root system is the underground part of the plant
• What are the two basic functions of the root system?

  Anchorage and absorption.
• Taproot system - consists of one main axis and has branching lateral roots
• Adventitious roots - may arise directly from the stem and they may also have their own lateral roots
• Fibrous root system - tap root is lost during early development leaving only the adventitious roots and their lateral roots
• Root hairs - small fuzzy projections arising from the taproot
• What is the modified part of the butress roots of kapok?

  adventitious

  
• What is the modified part of the climbing roots of philodendron?

  adventitious

  
• What is the modified part of pneumatophores of mangroves?

  Lateral roots
• What is the modified part of prop roots of corn?

  adventitious
• What is the modified part of the root nodules of makahiya plant?

  taproot or lateral
• What is the modified part of the stilt roots of pandan?

  adventitious
• What is the modified part of strangling roots of strangler figs?

  Entire root system
• what is the modified part of storage roots of carrot, radish, turnip, sweet potato, or cassava?

  taproot
• The primary root system is composed of the epidermis, ground tissue, and the stele
• Epidermis - outermost layer of parenchyma in the primary root
• Below the epidermis is the cortex, composed primarily of the ground tissue.
• In certain roots such as that of corn, the sub-epidermal layer is specialized into an exodermis
• Endodermis - Inner to the cortex and has thicker cell walls on its surface
• Inner to the endodermis is the outermost tissue of the stele called the pericycle
• Where do the lateral roots originate from?

  Pericycle
• What are found inner to the pericycle?

  primary xylem and primary phloem
• The core is mainly occupied by ground tissue called the pith
• Protoxylem - smaller and consists of tracheids and produce secondary wall earlier during root development
• Metaxylem - can be composed of tracheids and vessels and can grow larger before depositing secondary cell wall
• Exarch - patterns of xylem development where protoxylem tissue is found outer to the metaxylem tissue
• Endarch - patterns of xylem development where the metaxylem tissue is found outer to the protoxylem tissue
• Identify the number of protoxylem poles in the image

  A) Diarch

  B) Triarch

  C) Tetrarch

  
• The young Vicia sp. resembles the corn root in many ways. However, the former differs by having no exodermis, and less protoxylem poles
• Label the following in a corn root x.s.

  A) Epidermis

  B) Cortex

  C) Primary Xylem

  D) Primary Phloem

  
• Secondary growth involves the increase in the circumference and cross-sectional area of the plant organ
• Secondary growth is brough about by the activity of two lateral meristems. What are they?

  Vascular cambium and cork cambium.
• For the root, Vascular cambium arises from undifferentiated remnants of procambium and the pericycle
• For the cork cambium, it arises from the epidermis, cortex, endodermis or pericycle
• The vascular tissue system of the woody root is composed mainly of an inner secondary xylem and an outer secondary phloem
• The secondary vascular tissues of mature roots are separated by the vascular cambium
• For the tissue layers outside the cortex of the woody root, they are collectively called?

  Periderm
• The periderm contains the phellogen (cork cambium), which produces phelloderm (cork parenchyma) inwards and phellem (cork) outwards
• Label the following in an OLD ROOT x.s.

  A) Primary Xylem

  B) Secondary Xylem

  C) Secondary Phloem

  D) Vascular Cambium

  E) Cork Cambium

  
• Casparian strip - made of suberin that prevents apoplastic transport of substances