heliotropism

American  

[hee-lee-o-truh-piz-uhm, hee-lee-uh-troh-piz-uhm] / ˌhi liˈɒ trəˌpɪz əm, ˌhi li əˈtroʊ pɪz əm /

noun

1. heliotropic tendency or growth.

---

heliotropism British  

/ ˌhiːlɪəʊˈtrɒpɪk, ˌhiːlɪˈɒtrəˌpɪzəm /

noun

1. the growth of plants or plant parts (esp flowers) in response to the stimulus of sunlight, so that they turn to face the sun

---

heliotropism Scientific  

/ hē′lē-ŏt′rə-pĭz′əm /

1. The growth or movement of a fixed organism, especially a plant, toward or away from sunlight. Heliotropism can be easily seen in sunflowers, which slowly turn their large flowers so that they continually face the sun.

---

Other Word Forms

• heliotropic adjective
• heliotropically adverb

Etymology

Origin of heliotropism

First recorded in 1850–55; helio- + -tropism

Explanation

Heliotropism is a scientific term for a plant's tendency to turn toward the sun. Sunflowers are well-known for their heliotropism — they move in the sun's direction over the course of a day, tracking it across the sky. Have you ever noticed a house plant growing in the direction of a window? This is an example of heliotropism, when certain plants (and a few other organisms, like fungi) prefer to face the sun and grow in the direction of sunlight. This works with artificial lights as well, and in that case it's known as phototropism. We can trace heliotropism back to the Greek roots helios, "sun," and tropos, "a turn or change."

Example Sentences

Blocking blue, ultraviolet, red or far-red light with shade boxes had no effect on the heliotropism response.

From Science Daily • Oct. 31, 2023

The researchers have not yet identified the genes involved in heliotropism.

From Science Daily • Oct. 31, 2023

This unequal rate of movement, interrupted by pauses, and at first with occasional retrogressions, accords well with our conclusion that heliotropism consists of modified circumnutation.

From The Power of Movement in Plants by Darwin, Charles

The writer has shown that the experiments on the effect of acids on the heliotropism of copepods can be repeated with the same result in Volvox.

From Darwin and Modern Science by Seward, A. C. (Albert Charles)

The heliotropism of animals is identical with the heliotropism of plants.

From Darwin and Modern Science by Seward, A. C. (Albert Charles)