As Mrs. Whatsit takes the children into space, the air begins to get thinner. Before leaving, the children were given special flowers. They had to hold these flowers up to their faces so that they could breathe as the air became thinner:
"The atmosphere will continue to get thinner from now on. Hold the flowers up to your face and breathe through them and they will give you enough oxygen. It won't be as much as you're used to, but it will be enough."
All three children (Meg, Charles Wallace, and Calvin) remember the flowers and hold them up:
"Meg had almost forgotten the flowers, and was grateful to realize that she was still clasping them, that she hadn't let them fall from her fingers. She pressed her face into the blossoms and breathed deeply.
Calvin still held her with one arm, but he, too, held die flowers to his face.
Charles Wallace moved the hand with the flowers slowly, almost as though he were in a dream."