Describe modifications of stem with suitable examples.

(N/A) Stems of various plants undergo modifications to perform different functions other than their primary role of support and conduction.
$1$. Underground stems (Storage): These stems are modified for food storage and vegetative propagation. Examples include rhizomes (ginger,banana),corms (Colocasia),and tubers (potato). In potatoes,the tips of underground branches swell due to food accumulation,forming 'eyes' which are buds for new plants.
$2$. Supportive stems (Tendrils): In weak-stemmed plants,the stem modifies into thin,slender,and spirally-coiled structures called tendrils. These help the plant climb and attach to supports. Examples include cucumbers,pumpkins,and watermelons (Cucurbitaceae family).
$3$. Protective stems (Thorns): In plants like Bougainvillea and Citrus (lemon,orange),the axillary buds of the stem modify into woody,straight,and pointed structures called thorns. These protect the plant from browsing herbivores.
$4$. Photosynthetic stems (Phylloclades): In some plants like Opuntia (cactus),the stem becomes flattened or fleshy and green to perform photosynthesis,as leaves are often reduced to spines to minimize water loss.
$5$. Vegetative propagation stems: Runners (e.g.,grasses) spread horizontally in the soil to help in perennation. Offsets (e.g.,Eichhornia) are short,thick,lateral branches that produce new plants in aquatic environments.