The Romantic Story of the Highland Garb and the Tartan, published in 1924, and authored by J. G. MacKay and Norman MacLeod.
Scottish Clans and Their Tartans, published by W. and A. K. Johnston in Edinburgh. This little volume was originally published towards the end of the nineteenth century and was reprinted numerous times in the twentieth century. (I have one in my personal collection from 1943 and it's the 33rd edition). This one online is supposed to be from the early 1900s.