Agar is an essential thing to have when genetically engineering ancient plants.

JC screenshot - Agar cooking

Cook Gracilaria seaweed in a furnace to get Agar jelly

In order to make Agar jelly, you will first need to find some Gracilaria seaweed.

1x Gracilaria seaweed in a furnace = 1x Liquid Agar

Once you have some Liquid Agar, combine it with some Petri Dishes:

4x Petri Dishes + 1x Liquid Agar = 4x Petri Dish with Agar

JC screenshot - Petri dishes with agar

Craft petri dishes with Agar like so

These will become useful when making plant seeds...