These are letters and papers relating to North America chiefly from the official correspondence of the Gardens and the correspondence of its two directors, Sir William Jackson Hooker and Sir Joseph Dalton Hooker. There are 2 reels of letters from Asa Gray to the Hookers, in addition to other Gray letters elsewhere in the collection. A few letters (1787) from Americans to William Forsyth, superintendent of the Royal Gardens of St. James' and Kensington.

The largest portion of correspondence is with Charles Edwin Bessy on botanical matters, including botanical publications in the United States and Europe, and plants and shell specimens.

This is primarily a collection of letters, with some additional documents, concerning Young's interest in botany, geology, mineralogy, and natural history. There is information about Bowdoin College, where he studied under Parker Cleaveland. There is also much on the natural history of Maine, where he was the State Botanist in 1847-1849, and also on the Bangor Natural History Society. There are materials on Brazil in relation to Young's service there as the U.S. consul to Rio Grande do Sul from 1863 to 1873. There are also letters from his brother, John C. Young, and his sister, Sarah Augusta Young.