Endomycorrhiza, also known as arbuscular mycorrhiza, refers to a type of mutualistic symbiotic association between certain fungi and the roots of most vascular plants. The correct answer for the example of endomycorrhiza is option 'D', Glomus.

- What is Endomycorrhiza?
Endomycorrhiza is a mutualistic association formed between a group of fungi known as Glomeromycota and the roots of plants. It is the most common form of mycorrhiza, found in about 80% of plant families, including many important agricultural crops.

- Glomus and Endomycorrhiza:
Glomus is a genus of fungi that plays a significant role in forming endomycorrhizal associations. It forms mutualistic symbiosis with the roots of plants, where both the fungus and the plant benefit from the association.

- Mutualistic Relationship:
Endomycorrhiza is a mutualistic relationship, meaning both the fungus and the plant benefit from the association. The fungus colonizes the root cells of the plant, forming specialized structures called arbuscules and vesicles. These structures facilitate nutrient exchange between the fungus and the plant.

- Benefits for the Plant:
1. Increased nutrient uptake: The fungus extends its hyphae into the soil, greatly increasing the surface area available for nutrient absorption. This enhances the plant's ability to acquire essential nutrients, such as phosphorus, nitrogen, and micronutrients.
2. Enhanced water uptake: The extensive network of fungal hyphae helps the plant in absorbing water more efficiently, especially in drought conditions.
3. Disease resistance: Endomycorrhizal associations have been shown to enhance the plant's resistance to certain pathogens and diseases.
4. Improved tolerance to environmental stresses: Plants associated with endomycorrhiza exhibit better tolerance to various environmental stresses, including heavy metal toxicity, salinity, and extreme temperatures.

- Benefits for the Fungus:
1. Organic carbon supply: The plant provides the fungus with carbohydrates produced through photosynthesis. These carbohydrates serve as an energy source for the fungus.
2. Sheltered environment: The plant root provides a protected and nutrient-rich environment for the fungus to grow and reproduce.

- Conclusion:
Endomycorrhiza, exemplified by Glomus, is a mutualistic association between certain fungi and the roots of plants. This symbiotic relationship benefits both the fungus and the plant by enhancing nutrient uptake, water absorption, disease resistance, and tolerance to environmental stresses.