Frodo thinks that Sam is Spring itself. He watches as Sam coaxes life from the earth, as he wakes flowers and trees and vegetables and nurtures them into bloom and leaf and growth. Living things answer his call and come rushing back to life. Sam smells like good, clean soil, and new grass, and soft rain. Scars and damage are soon washed away in the renewal of Spring, healed and turned into something beautiful and growing. Sam is the dogged persistence of life, surging forward against all barriers. Sam is the promise of all that is to come.
Sam thinks that Merry is Summer personified, he has grown so gloriously shining and confident and joyous. His presence is warm and glowing and heartening, and when he passes through a room, hobbits (especially the lasses) turn and lean in toward him, as if to soak up his heat and light. Merry is giving and unhurried and celebratory, and if he has dark nights filled with violent storms, they do not show in the morning. They call Merry the Magnificent, now, and he shines down on the Shire in basking rays.
Merry thinks that Pippin is the very essence of Autumn. He even smells like it, all year round -- crackling leaves and apples and harvest and bonfires. He is a bracing, twirling gust of wind that comes crashing through the front door of Crickhollow and blasts straight back to the kitchen, leaving objects quivering in his wake. Pippin is all vibrant and varied colors, bristling in the wind. He is the call to adventure, to walking-trips and roopie games and cantering ponies. Pippin is the harvest of abundance, and his very presence satisfies those surrounding him.
Pippin thinks that Frodo is Winter. Sometimes he is the Winter of warm and cozy rooms with a heartening fire and a good cup of tea. Other times, he is the Winter of softly falling snow, making familiar landscapes achingly beautiful and strange and ethereal. And yet other times, he is the Winter of frozen waters and biting winds and black, black nights that seem to never end. The chill of Winter has seeped into Frodoís very bones, and even in the glory of Midsummerís Day, Pippin can see the frost clinging to him. Pippin is afraid that the only thing that can thaw Winter are the warm currents of the Sea.