Question for botanists

[Patrick]

(I know nothing of botany.)

Most plants grow upwardly. How do they "know" which way is up?

[TeaBag420]

Originally posted by Patrick
(I know nothing of botany.)

Most plants grow upwardly. How do they "know" which way is up?

No plants grow upwardly. However, many plants grow upward. Generally, plants grow away from their starting point. Many melons grow horizontally. Plants which grow downward tend not to be noticed, if indeed they survive.

[neutrino_cannon]

http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=upwardly

- up·ward·ly adverb

http://starryskies.com/try_this/plant_growth2.html

There you go.

[Kumar]

Negative gravitropism leads plants to grow up out of the Earth but growth of the shoot directly toward the sun is even more advantageous to a photosynthetic organism.

[MRC_Hans]

Negative gravitropism. Now, based on earlier experience, I have a nagging suspicion that you don't understand that yourself Kumar, but nevertheless, you are right. Most land plants can "feel" what is up and down. So, when you place a seed in the soil, even without light, the stem grows upwards and the roots grow downwards.

Hans

[Kumar]

"Phototropic and gravitropic responses share several properties. A stimulus (light or gravity) leads to unequal distribution of auxin. Elongation of plant cells is affected by a plant growth hormone called auxin. The change in auxin distribution almost certainly results from a lateral migration of auxin rather than from differential synthesis or degradation. Root or shoot bending is due to differential cell enlargement in response to differing auxin concentrations."