Sentence:  “Heavens!” exclaimed Nina, “the blue-stocking and the fogy!—and yours "are" pale blue, Eileen!—you're about as self-conscious as Drina—slumping there with your hair <WSD>tumbling</WSD> "à la" Mérode! Oh, it's very picturesque, of course, but a straight spine and good grooming is better.nb...” 
Meaning of the word marked with <WSD> tags:  To fall end over end; to roll.