I'm new to the game, but when I saw your question I went to my last savegame and invested a point in Alchemy.
Then I hovered an empty flask over some blueish mushrooms and the mushrooms disappeared. I think even the flask disappeared, and my character said: 'I'm obviously not skilled enough for this.'
So the picking up bit will have something to do with hovering an empty flask over them, but for successful Alchemy we'll need to know a little bit more. Have you tried the search option yet? Hopefully a more experienced alchemist will chime in...
