Final answer:
The proximity of veins in leaves is critical for efficient distribution of water and nutrients required for photosynthesis and plant growth. A dense venation pattern ensures a more effective delivery of these substances, which is essential for plant survival, especially in extreme environments.
Step-by-step explanation:
It is necessary for veins to be relatively close together in leaves because veins in plants, containing both xylem and phloem tissues, are crucial for transporting water, nutrients, and sugars throughout the plant. This vascular system allows for efficient water transport from the roots to the leaves for photosynthesis and sugar transport from the leaves to other parts of the plant.
In particular, leaves with a dense network of veins, such as those with reticulate venation in dicots or dichotomous venation in Ginkgo biloba, can more effectively distribute these necessary substances to all leaf cells. Additionally, in extreme environments, adaptations such as reduced leaf size and sunken stomata help to reduce transpiration and conserve water.