This 276-page book in French includes several essays and articles related to botany and astronomy in J. R. R. Tolkien's works of fiction.

In the botanical part, Stéphanie Loubechine studies several aspects of the symbolism of trees in Tolkien's stories and poems, focussing on the opposite and complementary roles of the Willow and the Birch. Alain Lefèvre, noting the apparent contradiction between the golden alfirin of Legolas' song in Lebennin and the white alfirin growing on funeral mounds, reinterprets them under the light of their likeness with the elysian amaranths and asphodels. Didier Willis analyses some of Tolkien's strategies in naming trees in his Elvish languages, trying to cast some light on the obscure lebethron tree mentioned twice in The Lord of the Rings. Finally, Lionel Pras applies his science of gardening to all invented trees of Middle-earth, commenting and discussing all we know about them.

In the astronomical part, Professor Kristine Larsen provides the most definitive and likely interpretation of Borgil, a star name (this is the French translation of an essay previously issued in Tolkien Studies (vol. 2, 2005). Didier Willis discusses possible astronomical interpretations for the Crown of Durin and tentatively interprets the repetition pattern in Gimli's Song of Durin under the angle of axial precession and its implications in historically dating the Tale of Arda. François Augereau and Didier Willis study the scientific implications in the definition of Durin's Day and the nature of the Moon-letters on Thror's Map in The Hobbit, providing an account of the structure of the Dwarvish calendar that can be deduced from them. Alain Lefèvre briefly discusses one of the little-known mentions about the fate of Tuor and Idril in one the many versions of the tale as presented in The Book of Lost Tales, which could possibly hint toward a representation of Mercury. François Augereau concludes this volume with a thorough study of all eclipse patterns in Tolkien's works, whether explicit astronomical phenomenons or implied literary and stylistic occultations, from Roverandom and The Father Christmas Letters to The Lord of the Rings and Morgoth's Ring.