I was at Kew last Monday, looking at archive correspondence from/to/about David Douglas. The first letter I picked up, dated March 23 (my birthday) 1835 was from John Douglas (DD's brother) to William Hooker at the Glasgow Botanic Garden. It was the first letter written by John after learning of his brother's death, far away in Hawaii, and he records his "distress at David's death".
This is the first time I've ever seen Douglas referred to in a family way - he's normally referred to as simply Douglas, or Mr Douglas or, after his stay in California, Dr Douglas. I thought that was really quite touching.
Incidentally, William Jackson Hooker and his son Joseph Dalton Hooker were the intellectual powerhouses of Kew throughout the 19th century. There is an excellent biography - the Hookers of Kew - which I commend to your attention, although if you go round nowadays asking for the Hookers of Kew you might get quite a different sort of attention.