Tropisms and Other Responses of Plants

Tropisms and Other Responses 

of Plants

Plants have senses and feelings

Dr Abe V Rotor

Here are some natural responses of plants to the environment:

- The flowers of Balibago (Hibiscus tiliaceus Linn), Family Malvaceae. open pure white in the morning gradually turning into pink towards the end of the day (photos); pongapong (Amorphophallus paeoniifolius),is one big flower in summer and all-shrub the rest of the year; fire tree (Delonix regia) "burns" only in autumn's season in the tropics. These are indeed manifestations of Nature's mysterious ways.

- Seeds germinate upward even if inverted; seedlings face and lean toward the source of light; cuttings (e.g. cassava) sprout with the same response. On the other hand, roots respond positively to gravity, forming a network counterpart of the plant's crown in size and dimension; aerial roots of vines, lianas, and epiphytes (e.g. orchids), though less distinct, generally follow this pattern.

- Forests form a "blanket" of trees or canopy with emergents jotting out sporadically, a typical characteristic of tropical rainforests; and together with shrubs, bushes, lianas, perennials, ferns, and the like, form a multi-storey composition. 

 

- Crop harvest increases when planted on East-to-West orientation, "following the sun". Increasing the rate of seeding increases yield only at a certain point, then declines drastically. Photoperiodism prevents certain plants (eg wagwag rice variety) from completing their normal life cycle; while vernalization enables crops (e.g. wheat in Siberia) to fit into the short crop season by induced dormancy .

  

Part 1 - Phototropism and Heliotropism*

Part 2 - Geotropism or Gravitropism

Part 3 - Thigmotropism - Response to Touch or physical Contact

Part 4 - Hydrotropism - Response to Moisture and Water Regime

Part 5 - Chemotropism - Response to Chemical Stimulus

Part 6 - Other Plant Responses

Part 1 - Phototropism and Heliotropism*

"We grow to the light like plants do." 

— A common botanical and philosophical observation on human nature. 

Sprouting bulbs of Lasona or Sibuyas Tagalog (Allium cepa L)

lean toward source of light.  Living with Nature Center AVR 2026

Have a window garden near the kitchen and Lo!

You've onion leek, kamote tops, and many. 

Let the sunshine in, while your plants look away;

Harmony is paradox, but that's nature's way.

 

Trees at the Center grow on three-storey design: ground plants and shrubs, 

main canopy layer, and the tallest, emergents. An arboretum however, is 

influenced by certain factors, like species composition, and pruning (right)

Photos by the author 2025

Trees like pets, are subject to their master's whim,

Else leave them to Nature's own housekeeping;

 We ask, where then does man, the guardian, come in? 

Just look at the dead valley and bald mountain.

Left, young sunflowers track the sun from east-to-west daily through heliotropism, but mature sunflowers stop moving and permanently face east. Sunflowers  by Vincent Van Gogh, a post-impressionism painting, shows young and old sunflowers all facing a common direction.

Mystery's never solved, books gather dust in the shelves;

scientists. philosophers, artists, bards themselves

search and claim in their own way, and will never agree;

 the sunflower follows the sun is Nature's own way, 

* Phototropism is a permanent growth response where a plant bends toward a fixed light source driven by the hormone auxin. Heliotropism is active solar tracking, where plant organs like flowers or leaves dynamically follow the sun from east to west during the day and reset at night. Also known as solar tracking, this behavior helps maximize sunlight absorption for photosynthesis, boosts plant growth, and attracts vital pollinators. Acknowledgement with gratitude: /Internet/Wikipedia

Part 2 - Geotropism 

Geotropism is response of plant growth to gravity. Roots show positive geotropism by growing down into the soil, while stems show negative geotropism by growing upward toward the air and light.

 

Dangling aerial roots of Ficus, relative of the balete (Ficus benjamina),

curtain the entrance gate of  Palacio del Gobernador, an old hispanic 

building in San Vicente, Ilocos Sur. Author is delighted with the

 rare specimen. 

Part 3 - Thigmotropism

Directional growth in which a plant responds to touch or contact 

with a solid object. It allows climbing plants to grip structures for 

physical support and helps roots steer around obstacles in the soil.

A classical example of this tropism is demonstrated by the makahiya,

literally "shy" in Pilipino.

 Makahiya (Mimosa pudica) makes a plaything for children and adults trying to steal a leaf without drooping, wishing almost anything in the world from love to fortune - if  they succeed. And no one will ever succeed in altering nature's gift to this shy plant. Special cells called pulvini control the drooping of the leaflets and the whole compound leaf, and restoring them fresh and erect once these cells are filled again with water.  The powder puff flowers attract bees and other pollinators without alarming the plant, thus insuring fertilization and production of seeds. 

 

A school girl hugs a heritage mango tree on her way home 

from school. Living with Nature garden.  San Vicente, Ilocos Sur

Hug a tree and feel its warmth, 

 it whispers, sings a lullaby;

it connects the living world

as one, with you and I. 

Part 4 - Hydrotropism

Aquatic plants exhibit amphibious characteristics, positive response to water in summer, and moves on land when the pond overflows.  Water loving plants (hydrophytes) like kangkong (Ipomea aquatica) clearly demonstrate this adaptation.

 Photo by the author at Gourmet Farm, Silang, Cavite.

Part 5 - Chemotropism

Roots of mangrove reach out for its nutrient needs

 in its natural habitat bordering an estuary or swamp. 

Mangrove is known for its adaptation to extreme 

conditions of the environment. Internet photo

Beneficial and harmful effects of chemicals on plants

Part 6 - Tropisms in Plants - Other Reponses

  

Trees at the Living with Nature Garden, photos by AVR 2025.

Tropisms in plants are shown in these images.  Can you cite 

specific examples in your area?

 

 Acacia trees tend to lean on the highway for light and space.

Photos by the author along Vigan-Laoag route 2023 

 

Dr Anselmo Set Cabigan, Ph.D. examines the flower of the enigmatic pongapong (Amorpophallus campanolatus). Samplings of Pine (Pinus insulares) adapt to 

lowland climate in Lipa, Batangas, a biological principle called acclimatization.

Photos by the author. 

  

ANNEX 1 - Disoriented seedlings exposed 

to RF (Radio Frequency) radiation.

The negative effects of EMR* on life is something that has been ignored by health officials and legislators for years. As cellphone subscriptions outnumber the total number of US citizens, more and more mobile phone towers are popping up around the globe. As the experts cautioned, it is extremely pertinent that further independent research is conducted to highlight the dangers of EMR.

Radiation disturbs tropism governed by auxin, plant hormone that dictates direction of growth (geotropism, towards gravity; phototropism, towards sunlight; thigmotropism, away towards or from touch) These abnormal behavior is specific and is not transmitted to the offspring, unless the genes have been impaired resulting in mutation.

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* EMR - a form of energy that travels through space as oscillating electric and magnetic fields perpendicular to each other and to the wave's direction. It moves at the speed of light and does not require a medium, meaning it can travel through a vacuum.

 

ANNEX 2 - Student Science Experiment Shows 

Plants Won’t Grow Near Wi-Fi Router

by Morgana Matus, 06/02/13

Garden cress (Lepidium sativum): left, exposed to Wi-Fi routers failed to grow, while the control grown in another room without Wi-Fi routers developed normally. © Kim Horsevad from Hjallerup School

Five ninth grade students from Hjallerup School in Denmark conducted a science experiment that elicited profound and shocking results about the effects of cell phone radiation. Their project was inspired by the observation that they had difficulty sleeping if their cell phones were next to their heads at night. They originally hoped to test the effects of a cell phone’s radiation on humans, but since their school did not have the necessary equipment to do so, they decided to experiment with radiation exposure on plants instead. Using two wireless routers that emitted about the same type of radiation as an average cell phone, they filled six trays full of the garden cress Lepidium sativum and placed them in a room with two routers, and then placed six trays of the plant in a room without Wi-Fi routers. The result of their experiment is shown in the above photo. ~