The Rose-Garden Game
Unfortunately this book is clearly a product of its times (1969) and it has some problems. The author is fond of the Mystic East, and finds a great deal to say about the metaphoric and psychological implications of roundness, beads, circles, roses, the repetition of prayers and so forth. A lot of the statements she makes are not backed up by any reference to sources. She definitely has her own ideas about the meaning of beads and their history, and I am skeptical of a lot of her conclusions, since they don't seem to me to be backed by any solid historical documentation.
It also shares a fault with many other popular books about the history of artifacts, which is that — as was common before the mid-1980s or so — it assumes without saying so that 19th-century popular culture is an essentially unchanged version of traditions that go back to the Middle Ages or earlier. We now know a lot more about how traditions are transmitted and where they come from, and it's generally agreed now that this was a highly romanticized view, powered by wishful thinking more than by any actual evidence. Nineteenth-century "tradition" can give us useful clues, but we can't assume these apply to any other century without checking them out. Wilkins relies on a lot of 19th-century material, which is certainly interesting, but has to be treated with caution.
That said, she does include direct quotes from some historical sources — for instance, she has more information about Lady Godiva's will than I've seen elsewhere — and she also reproduces quite a few photos, which are all footnoted as to source and include the dimensions of the rosary (yay!!). Some of her photos are of pieces I haven't seen any photos of anywhere else — the very drool-worthy emerald rosary from the Schatzkammer in Munich, for instance, and a couple of paintings that show people using the less common rosaries that use "disk" counters rather than beads.
As virtually the only source in English for many years, it has been relied on by many other authors, including Lois Sherr Dubin in her massive history of beads. But while it's still valuable (especially for its photos), there are now much better sources on the history of the rosary.
For the development of the rosary (as we now know it) in the middle 1400s, and its rapid rise in popularity, I would recommend Anne Winston-Allen's Stories of the Rose: The Making of the Rosary in the Middle Ages. She does not, alas, discuss the actual beads, but she thoroughly explains the ideas that came together to form the rosary, the people most responsible for its development, and the foundation of the first "rosary brotherhoods" in Germany.
For information about the actual beads, who made them, who bought them or gave them as gifts, how they were arranged and so forth, Ronald Lightbown's Medieval European Jewellery is the book to see. It was put out by the Victoria and Albert Museum and is now very hard to find except in a university library; it's also huge, heavy, out of print and very expensive (multiple hundreds of dollars, if you can find a copy at all). Its chapters are packed full of examples and citations, and the color photographs in the back are utterly gorgeous.
The Rose-Garden Game: A Tradition of Beads and Flowers, by Eithne Wilkins. (1969, Herder & Herder, no ISBN)
Stories of the Rose: The Making of the Rosary in the Middle Ages, by Anne Winston-Allen (1997, Pennsylvania State University Press, ISBN 0-2710-1631-0)
Medieval European Jewellery, by Ronald Lightbown (1992, Victoria & Albert Museum, ISBN 0-9481-0787-1)