The thorn hits (rolled 19), but the mushroom is not affected.
Round 225: The mushroom floats to 45N15E10Z. The thorn feels something try to assault his mind, but resists (rolled 11 Will save vs. DC 8). The thorn also feels like he is being tugged upward, but keeps his footing (rolled natural 20 Ref save). He does, however, manage to breathe in particles that are not good for him (rolled 6 Fort save), taking 3 points of Dexterity damage. The thorn's Dexterity is down to 11.
(How often does one have to make one of each kind of save in the same round against the same creature?)