Hathi Trust has the 8 volumes of Herbier général de l'amateur published between 1816 and 1827 at this link. The text is in French but the illustrations (Bessa’s work) are the draw even if you read French. This is a colorful way to spend a few winter hours. I’ve made a slide show of some sample images from each volume.
The main author has a very short entry in Wikipedia; he was evidently a physician and botanist. He lived from 1774 to 1849 when there was a lot of botanical discovery and popularization going on. I was surprised that these volumes were not listed in the ‘selected works’ section of the Wikipedia entry. They were mentioned in the entry for Bessa and an article about a 2008 exhibition at the Hunt Institute for Botanical Documentation. The artist is better known than the author!
Another oddity – on the title page it references Mordant de Launay as ‘first author.’ I found a web page from a rare book seller that explained: The first 11 parts of volume 1 were by Mordant de Launay and the rest were the work of Loiseleur-Deslongchamps. The book seller lists the 8 volumes for $16,250. What a value the institutions that are scanning and making the volumes available provide for us to enjoy online – with no worries of damaging a fragile book!