Question

Which of the following is not a stem modification?
A. Pitcher of Nepenthes
B. Thorns of citrus
C. Tendrils of cucumber
D. All of the above

Answer 1

Changes in aerial stems, vegetative buds and plant floral buds perform functions such as climbing, protecting and synthesizing food propagation vegetative.

Complete answer:
Some species of plants have modified stems which are particularly suitable for a particular habitat and environment. An adjustable rhizome is a horizontally underground stalk that has nodes and internodes. Some plants, including ginger and ferns, may have vertical shoots from the buds on the rhizome. Corms are more round and fleshy than rhizomes. Corms contain food stored for winter survival of some plants. Stolons are stems that run nearly parallel to the ground, or below the surface, and at the nodes may grow new plants. Runners are a form of stolon that runs over the ground and at different intervals produces new clone plants at different nodes. Tubers are modified stems that can store starch, as seen in the potato. Tubers appear as swollen ends of stolons and contain several rare or unintended buds.

Nepenthes are usually referred to as pitcher plants. It is a plant that is insectivorous. In this plant a pitcher like structure is transformed from a leaf lamina that traps insects.
Thorns are modified branches that tend to shield the plant as rough, woody, sharp outgrowths. The thorns of citrus are modified stems.
Tendrils are slender, twined strands that allow a plant to seek support by climbing to other surfaces. >These may grow either from the axillary bud or the stem's terminal bud. The tendrils of cucumber are the modification of stem.

Thus, the correct answer is option A. i.e., Pitcher of Nepenthes.

Note: Leaves can be modified as spines that minimize water loss and can also function as a shield. Some are modified into tendrils to provide aid to the plant. Some leaves are thick and help to store water. Any of them are altered to capture and digest insects.