Final answer:
Autumn is called the 'season of mists and mellow fruitfulness,' a term from John Keats' poem, signifying the harvest time and abundance of fruit along with misty conditions and transformation in nature's colors as the leaves change.
Step-by-step explanation:
The phrase “season of mists and mellow fruitfulness” is famously coined by the renowned poet John Keats in his ode “To Autumn.” Autumn is often characterized by its atmospheric conditions, such as mists that provide a soft, damp cloak over the landscape, particularly in the morning and evening. The 'mellow fruitfulness' refers to the time of harvest, when fruits like apples and grapes become ripe and are plentiful. The season brings about a sense of abundance and maturation that Keats poetically describes.
Additionally, the vibrant colors of changing leaves, as described in subsequent literature, further contribute to the autumnal palette. Shorter days trigger leaves to change color, as noted in the explanation of Figure 7.14.1. Leaves like those of maples and oaks become brilliant hues of orange, red, and yellow, due to the reduced production of chlorophyll, which allows other pigments to show through. This transformation sets the scene for what many perceive as the quintessential autumn atmosphere.
The combination of agricultural abundance, the transformation of nature's colors, and the particular climate conditions help to sum up why autumn is afforded such a poetic characterization. It captures the essence of a time both plentiful and poignant, as summer gives way to winter, and the cycle of growth and harvest comes full circle.