Sword Coast Adventures
This is big and heavy tome which is filled with writings in Druidic code mixed with various plant pictures and schematics.
This book was written by exiled druid Belak The Outcast.
The book is result of very long research performed by him. Main topic is adaptation of plants from surface to grow in Underdark, using light of luminescent fungus.
Out of sheer curiousity Vordin decided to take it.