How are onion scales classified anatomically?

Anatomically, onion scales are classified into fleshy (inner) scales and dry (outer) scales. The fleshy scales are thick, succulent leaf bases modified for food storage; they contain parenchyma cells filled with starch and sugars. 

These layers are living tissues actively involved in metabolism. The outer dry scales are older, dead epidermal layers that become papery as they lose moisture and lignify. 

They form the bulb’s protective tunic, shielding it from pathogens and dehydration. Each scale originates from the base of the stem plate and overlaps concentrically, forming the bulb’s characteristic layered structure. 

The transition from fleshy to dry scales represents the onion’s aging and dormancy stages. This differentiation ensures the bulb can store nutrients efficiently while maintaining protection, allowing survival during unfavorable environmental conditions.