I bought some mushrooms that I really like, but they are very expensive. They only sell the caps and stalks. I'm pretty sure I can't grow clones from this, but I'd like someone to verify this. These shrooms are super yummy!
you *can* get a clone growing on agar from a storebought mushroom.
portobellas can be done, basically you take a peice of flesh from the inside of the cap (after splitting it).
if you are serious about fungi cultivation, get the Paul Stamets book "the mushroom cultivator"