Different Plasmids and Gene Tonics become available at different points of the game. Often, Plasmids will cost less ADAM when bought at a Gatherer's Garden at a later point in the game, but a tonic always has the same price. Many of the tonics can be found for free but will show up at Gatherer's Gardens on some subsequent levels if not picked up as free loot. Generally (with few exceptions), each Gatherer's Garden has one Plasmid Slot, one Tonic Slot for each category, one Health Upgrade, and one EVE Upgrade for sale.