Paper Mario: The Origami King starts off with one of the more confusing tasks if you're not aware of what you're doing.
In traditional RPG fashion, you need to collect an item to progress through the story and if you're not one for exploring and looking around you'll often miss key items like this.
Such is the case with the Soul Seed necessary to save Ol' Grandsappy.
Here's how to get the Soul Seed and save him.
How To Get The Soul Seed In Paper Mario: The Origami King
If you've met Ol' Grandsappy and haven't grabbed the Shriveled Seed, you're going to need to backtrack.
In the area, before you meet him, the Shriveled Seed is located in a golden ball with a vine attached.
Mario is obviously too short to reach, so you'll need to whack the tree it's connected to - this will release a golden shard and activate a magic circle.
Stand on the magic circle to activate your 1000-fold arms and pull on the vine, releasing the Shriveled Seed.
Head past Ol' Grandsappy and towards the lake. Go all the way around the lake's path until you reach the centre where a small platform reaches into the lake.
You'll be prompted to interact with the lake and eventually your items inventory will open, allowing you to drop the Shrivelled Seed into the lake.
This will convert it into the Soul Seed. It's worth noting if you have grabbed the Shrivelled Mushroom and Fire Flower, you can do the same with these to restore them back to normal.
Head back to Ol' Grandsappy and give him the Soul Seed. He'll be delighted, breaking out into a song and dance before turning into a huge healthy tree.
This process will be necessary to continue on with the story, as the trees and grass will open and allow you to progress to the next stage of the game.