Auxin action

thumb|The light from the lamp (1.) functions as a detectable change in the plant's environment. As a result, the plant exhibits a reaction of phototropism—directional growth (2.) toward the light stimulus. thumbnail|Auxin distribution controls phototropism. 1. Sunlight strikes the plant from directly above. Auxin (pink dots) encourages growth straight up. 2, 3, 4. Sunlight strikes the plant at an angle. Auxin is concentrated on one side, stimulating growth at an angle from the preceding stem. thumb|Phototropism in Solanum lycopersicum.

alt=This is an image taken of a tree from Central Minnesota. The tree was on the face of a hill and had blown over in a storm or fell over due to erosion in the soil surrounding it. The tree continues to grow however, and because it was horizontal, its growth exhibits gravitropism which can be seen in its arched growth.|thumb|300x300px|Example of gravitropism in a tree from central Minnesota. This tree has fallen over and due to gravitropism exhibits this arched growth. thumb|300px|right| Gravitropism maintains vertical orientation of these trees. These trees, typical of those in steep subalpi

plant growth pattern

right|thumb|Redvine (Brunnichia ovata) tendrils coil upon contact.

thumb |400px |Daisies (Bellis perennis) face the Sun after opening in the morning and will follow the Sun through the day. Heliotropism, a form of tropism, is the diurnal or seasonal motion of plant parts (flowers or leaves) in response to the direction of the Sun.

thumb|right|228px|

plant cell ability to expand quickly at low pH