Biology · Morphology of Flowering Plants · NEET
Bougainvillea thorns are a modified STEM. They develop from the axillary bud, so they arise in the axil (the angle between the leaf and the stem). This is a very common NEET trap because they look like sharp leaf-spines, but they are stem in origin. NEET 2017 asked this exact fact and the answer was Stem.
Both come from buds (axillary or terminal), but they do different jobs. A stem tendril is thin, long, and spirally coiled and helps a weak plant climb up a support (grapevine, cucumber). A stem thorn is short, hard, woody, and pointed and protects the plant from animals eating it (Bougainvillea, Citrus). Same origin, different shape, different function.
Yes. In Citrus, the thorns are modified axillary buds, so they are stem thorns used for protection. Do not confuse this with the fact that Citrus also shows polyadelphous stamens in its flower; those are two separate NEET facts about the same plant.
Grapevine (Vitis) tendrils are STEM tendrils, because they arise from the axillary bud. Pea (Pisum) tendrils, by contrast, are LEAF tendrils (modified terminal leaflets). NEET loves to test this pair: grapevine = stem tendril, pea = leaf tendril.
Check its position. If the coiled tendril or the pointed thorn comes out from the axil of a leaf (the axillary-bud position) or from the tip of the stem (terminal bud), it is a stem modification. Stem modifications keep the bud, node and axil pattern, which leaf modifications do not.
In Bougainvillea thorns are the modifications of:
Identify the correct set of statements: (a) The leaflets are modified into pointed hard thorns in Citrus and Bougainvillea (b) Axillary buds form slender and spirally coiled tendrils in cucumber and pumpkin (c) Stem is flattened and fleshy in Opuntia and modified to perform the function of leaves (d) Rhizophora shows vertically upward growing roots that help to get oxygen for respiration (e) Sub-aerially growing stems in grasses and strawberry help in vegetative propagation.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. Both develop from buds — usually the axillary bud, sometimes the terminal bud. They differ only in shape and function: tendrils are thin and coiled for climbing, thorns are hard and pointed for protection.
Grapevine (Vitis), cucumber, pumpkin, watermelon, and gourds. These are weak-stemmed climbers that use thin coiled tendrils to hold a support.
Bougainvillea and Citrus (lemon). Their thorns are hard, pointed and protect the plant from grazing animals.
A thorn is a modified STEM (hard, pointed, from a bud), as in Citrus and Bougainvillea. A spine is a modified LEAF (or part of a leaf), as in Opuntia. NEET tests this difference directly.
No. Grapevine tendrils are stem tendrils (from axillary buds). Pea tendrils are leaf tendrils (modified terminal leaflets). Same look, different origin.
