Why is endodermis also called the starch sheath in dicot stem?

abundantly filled with starch grains.

Structural Features:

Endodermis in Dicot Stems:

• Innermost layer of cortex (boundary between cortex and stele)
• Single-layered, barrel-shaped cells
• No intercellular spaces (compactly arranged)
• Living cells with prominent nucleus
• Rich in starch grains (amyloplasts)

Contrast with Root Endodermis:

Feature	Stem Endodermis (Starch Sheath)	Root Endodermis
Casparian strips	Absent or poorly developed	Prominent (suberin bands)
Starch grains	Abundant	Usually absent or minimal
Function	Starch storage, barrier	Selective barrier for water/minerals

Physiological Role of Starch Storage:

• Energy reserve for meristematic activity
• Osmotic regulation
• Indicator of photosynthetic efficiency (starch accumulates when photosynthesis exceeds translocation)

Detection Method:

• Iodine test (I₂-KI solution) turns endodermal cells blue-black due to starch-iodine complex