What has one horn and gives away milk every day?

In winter's crisp air, I take flight, Gaining might as I roll with delight. Cold in the making, But warmth I'm faking, A round delight with pure, fluffy white.

I help plants climb up toward the sky, I’m like a wall, but holes go by. I’m criss and cross, a wooden net, What am I that flowers can’t forget?

I stand where I’m built, and don't step aside. Visible from distance, from far and from wide. Clocks, bells, or signals may mark the hour. Call me by name, I am a ...

Through towns and fields I chug along, a rolling line, both long and strong. With echoes deep and steady beat, I hum along on iron feet.