Question

In humid climate, presence of spines in shrub is

Answer 1

Hint:-Leaves or parts of leaves are sometimes modified for special functioning such as for climbing and attachment to the substrate, storage, protection against predation or climate, etc.

Complete answer:
Spines are modified leaves. In cacti, they're transformed leaves which protect the plant from herbivores, radiating heat from the stem during day time while collecting condensed vapour in the dark.
Some desert plants, like stoneplants and aloe, develop succulent leaves for water storage. The foremost common variety of storage leaves are succulent leaf bases of underground bulbs that function water- or food-storage organs or both. Many nonparasitic plants, epiphytes absorb water through specialized hairs on the surfaces of their leaves. The shoot system is modified for functions like climbing, protection, adaptation to arid habitats, and water or food storage. These modifications involve structural and shape changes to the stem and also the reduction of the leaves to small scales. Within the passion flower and grape axillary buds develop as tendrils with reduced leaves and suppressed axillary buds.

In Cactaceae, spines are a modified leaf lacking plant tissue that arise and multiply from the areoles and detach easily. They’re classified into central spines located centrally on the areola and radial spines round the margins, they'll be stout and woody or fine and hair-like, woolly, bristly, needle-like, barbed, hooked or curved and variously coloured. Cacti are identified primarily by their spine cluster morphology. They protect the fat stem against some predators, whether or not inefficiently, but their most vital function is to condense atmospheric moisture from dews, fog and rain (spines operate as a drip tip) in order that they drip to the bottom of the plant for uptake by the superficial rootage.

Note:- Thorns are the modifications of an axillary shoot system in which leaves are reduced and the stems are heavily sclerified and grow for less than a limited time (determinate growth). Thorns appear to safeguard the plant against herbivores. Examples- Bougainvillea (Nyctaginaceae), where the thorn is modified inflorescence.