His second great undertaking was _L'Illustration des Genres_ (1791-1800), with a supplement by Poiret (1823).
Cuvier speaks thus of these works: "_L'Illustration des Genres_ is a work especially fitted to enable one to acquire readily an almost complete idea of this beautiful science.

The precision of the descriptions and of the definitions of Linnaeus is maintained, as in the institutions of Tournefort, with figures adapted to give body to these abstractions, and to appeal both to the eye and to the mind, and not only are the flowers and fruits represented, but often the entire plant.

More than two thousand genera are thus made available for study in a thousand plates in quarto, and at the same time the abridged characters of a vast number of species are given.
"The _Dictionnaire_ contains more details of the history with careful descriptions, critical researches on their synonymy, and many interesting observations on their uses or on special points of their organizations.

The matter is not all original in either of the works, far from it, but the choice of figures is skilfully made, the descriptions are drawn from the best authors, and there are a large number which relate to species and also some genera previously unknown." Lamarck himself says that after the publication of his _Flore Francaise_, his zeal for work increasing, and after travelling by order of the government in different parts of Europe, he undertook on a vast scale a general work on botany.
"This work comprised two distinct features.

In the first (_Le Dictionnaire_), which made a part of the new encyclopedia, the citizen Lamarck treats of philosophical botany, also giving the complete description of all the genera and species known.