A sap run is the sweet goodbye of winter. It is the fruit of the equal marriage of the sun and frost.

In this quote, John Burroughs, an American naturalist and essayist, uses the metaphor of a sap run to symbolize the transition from winter to spring. A sap run occurs when the weather warms enough for the sap in maple trees to flow, a process that typically takes place in early spring. Burroughs poetically describes this natural event as the "sweet goodbye of winter," suggesting that the sap run marks the end of the cold, harsh season and the arrival of the more vibrant and life-filled days of spring.

The phrase "the fruit of the equal marriage of the sun and frost" underscores the delicate balance between sunlight and frost that creates the sap run. Burroughs personifies the forces of nature, implying that the warmth of the sun and the lingering chill of frost work together in perfect harmony, much like a marriage. This "equal marriage" represents the interconnectedness of opposing forces in nature, each contributing equally to the final result—the flowing sap that nourishes the trees and signals the arrival of new life.

Burroughs’ use of the word "fruit" here is symbolic, as it refers to the outcome or result of this natural union between the sun and frost. Just as a marriage produces something greater than the sum of its parts, the sap run is the product of two seemingly opposite forces, working together to bring about the renewal of the natural world. This imagery reflects Burroughs’ appreciation for the cyclical and harmonious processes of nature.

Ultimately, the quote reflects Burroughs' deep connection to the natural world and his ability to find beauty in its subtle changes. He emphasizes the way natural forces, such as temperature fluctuations, work together to create something sweet and nourishing, symbolizing the return of life and growth after the harshness of winter. It serves as a reminder of nature’s ability to create balance and harmony, even in the most seemingly opposite forces.