Here's why:

* Mesophyll: This is the inner tissue of the leaf where photosynthesis takes place. Chloroplasts, the organelles responsible for photosynthesis, are concentrated in the mesophyll.

* Photosynthesis: During photosynthesis, plants use sunlight, water, and carbon dioxide to produce glucose (sugar). This glucose is then converted into starch for storage.

* Starch Storage: Starch is a complex carbohydrate that provides energy for the plant. It's stored in the mesophyll cells until it's needed.

So, while other parts of the leaf might contain small amounts of starch, the mesophyll is the primary location for starch storage due to its role in photosynthesis.