How are stem modified?

Explanation:

Stem or its branches get modified into green thread like leafless structures called tendrils which are meant for climbing. These may be branched or un-branched. A scale leaf is always present at the point of branching of the tendril.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]