There are potions in the lab which can give a clue on the correct order. There is 1 (red) health potion, 2 (green) poison potions, 3 (blue) mana potions and 4 (yellow) stamina potions. Press the coloured buttons in that order to open the door.
I actually picked up the potions looting the room before I moved the bookcase out of the way to reveal the door. Fortunately I only needed a few attempts to guess the correct sequence (I assumed there would be some pattern).
Others have missed one or more of the Raanaar books, and I don't recall anyone posting about not being able to read the one on summoning. The required book is in the north west corner of the library, and states;
Book of Basic Summoning [Mushrooms are not listed in this book, but you find these entries under the letter 'M'...]
Morphology - Suitable Informer: Mutant, Necessary Components: Virgin Blood, Imp Toe, Sulphur, Protection Rune: Water
Mycology - Suitable Informer: Imp, Necessary Components: Feynur-Potion, Kohar Root, Spider Leg, Protection Rune: Wisdom
Mythology - Suitable Informer: Gargoyle, Necessary Components: Cyclops-Eye, Fairy Dust, Bat-Wing, Protection Rune: Lightning