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The Botany Lab is a room inside of the Haunted Towers in Luigi's Mansion: Dark Moon. The Botany Lab can be accessed by taking the door on the second floor of the Toolshed Stairs. Inside the Botany Lab, there is a large containment tube with a sprout. Connected to this tube is a large red machine similar to the one from the Water Supply. This machine can be activated to have water flowing through the pipes. On the other side of these objects are tables with flasks and test tubes with green and red liquid. A bucket sits on one of these tables and a purple flower as well as a wilted sprout are found to the right of these tables. The door on the right takes Luigi back to the Toolshed Stairs. After watering the sprout in the center of the room, Luigi can access the Seedling Laboratory from this room as well.
In B-2: The Pinwheel Gate, Luigi needs to go to the Botany Lab in order to create a way to the Seedling Laboratory. After revealing the missing pipe with the Dark-Light Device and capturing the Spirit Balls, activating the large machine causes the sprout in the middle to grow into a large stalk that reaches into the Seedling Laboratory. The poster to the left of this machine can be torn off for money and ten coins are located behind the machine. The poster yields no money in other missions. During B-Bonus: Hostile Intrusion, the Botany Lab might be one of the rooms infested with ghosts.
Starting on B-2: The Pinwheel Gate and most missions after, Luigi can use the water running from the pipes to fill the bucket on the table. Watering the wilted plant and flashing it with the Strobulb causes it to spit out an emerald.