The arte of manipulating biological processes. For instance, speeding up or slowing a creatures natural healing or a plant’s growth. More advanced forms can directly affect a sentient being’s hormonal balance to influence emotions and reactions or even induce halucinations.
Spells tap into the user’s own nutritient and chemical energy stores. Beginners typically must balance this out by eating substantially more than would be typical for their body. Experienced users, however, learn to photosynthesize. But if sunlight is not strong enough to sustain a spell, they are known to be able to leech off their surroundings. Either passively by drawing in all of the stray particles and nutrients in the environment, or directly by forcibly stealing from living matter.