If a plant's leaves only contained the vascular tissue xylem, then it will not be possible for the plant to absorb carbon dioxide. As carbon dioxide is required for photosynthesis to occur, this means that the process of photosynthesis will not take place. As a result, the plant will not be able to produce food as photosynthesis is the process by which plants make food. This will result in the plant to die eventually in the end due to lack of food.
