These letters are primarily to Sir Charles James Lyall, concerning botanical terminology as it relates to specimens from India. There are also a few letters on miscellaneous subjects from Thiselton-Dyer.

These are mainly letters written from British botanists to James and William Sowerby concerning flowers and botany in England. Most of the correspondents are represented by only one letter and include Charles C. Babington, William H. Baxter, Joseph D. Hooker, Daniel Oliver, and W. T. Thiselton-Dyer.

The collection is primarily professional letters written to Russell, but there are also a few letters from his wife and a few by him. There is also an autobiographical letter written by Russell. Most of the correspondence pertains to the Royal Meteorological Society, snow crystals, dew, frost, hail, fog, etc. Russell had wide-ranging interests, however, and some of his non-scientific concerns appear in the letters.