Spots dark purple, galls glandular, formed of papillate, pyriformly swollen epidermal cells ... which swell into large pyriform sacks, whose surface is raised in large, conical, scattered papillae. To the naked eye the swollen cells look like purple glands, which are often so abundant as to nearly cover the surface of the leaves, and remind one of the so-called species of Erineum. Each cell contains from
one to three resting spores which are small in comparison with the host-cell ...

- Farlow, W.G.: (1885) The Synchytria of the United States^©