Coordination method in plants

Chemical only (phytohormones) — no nervous system

Growth-promoting hormones

Auxins, gibberellins, cytokinins

Growth-inhibiting hormones

Abscisic acid; ethylene promotes ripening/abscission

Synergism example

Auxins + gibberellins

Antagonism example

Auxins + abscisic acid

Tropism

Growth movement, directional stimulus (e.g. light, gravity)

Nastic movement

Movement, non-directional (diffuse) stimulus, e.g. Mimosa

Tactic movement

Whole organism/motile cell moves toward/away from stimulus

Shoots & light/gravity

Positively phototropic; negatively geotropic

Roots & light/gravity

Negatively phototropic; positively geotropic

Short Day Plants

Flower when dark period exceeds a critical length

Vernalization

Flowering triggered by exposure to low temperature