CONCEPT:The PETIOLE is present at the base of the leafIt is basically the STEM of a leafThe petiole help hold the blade to light.Phyllode is a modified petiole.Explanation:DESERT plants have to withstand long dry spells and intense high temperatureHence the plant parts get modified to help prevent loss of excess waterFollowing are some examples:Roots are very long so they can penetrate deep in search of waterThe stem is green and fleshy and performs the function of photosynthesisLeaves are reduced to spines that prevent grazing as well as reduce evaporative loss of water through transpirationPetioles of leaves are modified in plants like Acacia gets modified to green vertical STRUCTURES called phyllodesThey carry out photosynthesis in Acacia as leaves are reduced or absentThey have very few stomata hence transpiration is minimumTranspiration is the evaporative loss of waterIt takes place through stomata, the same organ required for gaseous exchange for photosynthesis⇒ Phyllodes are found in acacia.