The correct answer is option 4: Fertilization. Fertilization is the process in plants where the sperm from the pollen combines with the egg to form a seed. This process is not directly influenced by light as it occurs within the reproductive organs of the plant.

Option 1: Flowering is directly influenced by light as plants use photoperiodism, a physiological response to the duration of light received, to regulate when to flower.

Option 2: Photosynthesis, the process by which plants convert light energy into chemical energy, is directly dependent on light.

Option 3: Transpiration, the loss of water vapor from plants, is indirectly influenced by light as it increases with higher light intensity, leading to increased evaporation of water from plant leaves.

Therefore, option 4 is the only event in a botanical garden that is not directly influenced by light.