LONDON — Last month the historian Sarah Whittingham nearly tripped over a rope blocking access to a Victorian house museum parlor here. “I’m so drawn to it,” she said, referring to the room’s bay window, an 1870s protruding glass case originally meant for sheltering ferns.

A staff member at the brick town house, 18 Stafford Terrace in the Kensington neighborhood, let Ms. Whittingham step over the rope, and she wound past the overstuffed furniture to study the window closely. The interior looks much as it did when the home’s owner, the cartoonist and photographer Linley Sambourne, lived there.

Ms. Whittingham, the author of the new book “Fern Fever: The Story of Pteridomania” (Frances Lincoln), explained that Sambourne’s wife, Marion, recorded in her diaries how often she “did fern cases.”...