Base notes form the foundational essence in the structure of perfumery, which also includes top and middle notes. Emerging last in the fragrant narrative, base notes leave a long-lasting impression even after the initial scents have faded. 

These notes, characterized by their depth and richness, can range from woody materials like vetiver and sandalwood, resins like amber, and sensual musks, to the comforting aroma of vanilla. Their large molecules ensure they evaporate slowly, making them enduring. They act as fixatives, enhancing the perfume's longevity and controlling the evaporation rates of the more fleeting top and middle notes. 

Base notes have a psychological facet, too, tapping into our deep-seated emotions and memories, offering more than just a sensory experience. In the world of perfumery, while top notes grab immediate attention and middle notes define the structure, the base notes provide stability, depth, and long-lasting resonance, much like the roots of a tree anchor its entirety. Base notes are crucial in perfumery, creating a deep, enduring memory of the fragrance and underscoring the olfactory journey's intricacies.