u/eldritchcorvid

I'm looking for books, (preferably free) online courses, or other resources to get a basic overview of botany.
I'm writing a story where one of the main characters is a late 19th century botanist studying taxonomy and breeding, and wanted to get a basic understanding of how plants work before writing him and his world. I'm looking for both the kind of stuff you'd learn in a contemporary university course but also, if possible, historical sources from the 19th century or a historical overview of the field as a whole. Kinda specific but any direction would be appreciated!