https://www.kew.org/science/our-science/projects/joseph-hooker-correspondence-project

"Sir Joseph Dalton Hooker (1817 – 1911) was a trailblazing botanist and explorer and Kew’s second Director. Detailing plant diversity and economic botany throughout his many expeditions, he remains an influential figure to modern botanical science. 

"During his career he was also a prolific correspondent, writing to family, friends and colleagues, including Charles Darwin, and we are fortunate to hold an extensive archival collection at Kew. The Joseph Hooker Correspondence project is working to make his letters held in Kew’s archive, and other institutions’, available online. The project originally began with a partnership between Kew and the University of Sussex to produce digital images and full transcriptions of Hooker's Indian letters. Staff at Kew are continuing the project with the digitisation and transcription of further series of Hooker's correspondence. A team of expert remote volunteers transcribe the letters.

"The formation of this online repository, comprised largely of previously unpublished archive material, is intended to facilitate academic research in such fields as botany and other natural sciences, horticulture, British imperialism, garden history, the history of science and the history of the Royal Botanic Gardens, Kew. Kew also hopes to bring knowledge of Joseph Hooker to a wider audience and to extend awareness of the extent and significance of his work."

"Currently available online are:
•    Letters from Hooker’s Expedition to India (1847-1851), including accounts of his pioneering exploration and plant hunting in the Himalayas.
•    A series primarily composed of letters from Hooker to pre-eminent American botanist Asa Gray, with whom he went on a plant hunting tour of America in 1877 and shared a lifelong scientific dialogue.
•    Letters written by Hooker during his time as assistant surgeon and unofficial botanist to James Clark Ross’s expedition of discovery to Antarctica (1839-1843)
•    Other letters have been digitised and transcribed and will be available shortly.." (accessed 10-2021)

[Start date of this project is not posted on its website; to fit this into the chronology I have estimated the date at 2010.]