Here's why:

* Efficiency: Starch is a highly compact and efficient way to store large amounts of glucose. It's a long chain of glucose molecules, making it less reactive and more stable than free glucose.

* Solubility: Starch is insoluble in water, which prevents it from drawing water into the plant cells and causing osmotic pressure issues.

* Accessibility: When the plant needs energy, it can easily break down starch back into glucose. This process is catalyzed by enzymes, making it readily available for use.

While starch is the primary storage form, some plants may also use other forms of glucose storage in smaller quantities, such as:

* Sucrose: A disaccharide (two glucose molecules linked together) that's readily transported within the plant.

* Fructans: Chains of fructose molecules, found in some plants like onions and garlic.

Overall, starch is the dominant and most efficient way for most plants to store glucose.