10 Examples of Positive and Negative Tropicalism

The tropism (both positive and negative), refers to the growth or change of direction of development of an organism and especially of a plant or being a plant, in response to a given environmental stimulus.

If the organism moves in favor of the stimulus, it will speak of positive tropism. If instead it does it in the opposite direction, it will speak of negative tropism. For example: positive hydrotropism, negative phototropism.

Types of tropism

We already know that a tropism will be positive or negative according to its orientation for or against the environmental stimulus considered. However, there are several types of tropisms according to the very nature of the stimulus, namely:

Difference between nastias and tropisms

Tropisms, which are sustained reactions to permanent stimuli, should not be confused with nastias, which are also movements of plant organisms, but focused on specific organs and ephemeral and diffuse character. The latter are active and reversible movements, the tropisms, on the other hand, are not, since they imply the definitive form of the organism.

An example of nastia are the sleepy plants (Mimosa pudica), which close their leaves when touched, to avoid being damaged.

Examples of positive tropism

1. Positive hydrotropism. Ficus are famous for migrating their roots towards water sources, lifting the pavement of the streets and breaking pipes in the process, so planting them in the vicinity of houses.
2. Positive phototropism. Sunflowers are known for their ability to literally turn to face the sun. That way they guarantee constant access to the sunlight they need. According to some experts, however, since it is not a form of growth, it would not be phototropism as such.
3. Positive geotropism. No matter how we sow a seed, the roots will always go according to the force of gravity, as this way the plant makes sure that they go to the ground and receive the nutrients necessary to continue their growth process.
4. Positive thigmotropism. Vines and climbing plants react to the presence of solid objects by growing around them and expanding on their surface. This means that many can literally suffocate others, robbing them of light and CO₂ what do you need.
5. Positive aerotropism. The plant known as the "bad mother", "spider" or "love tie" (Chlorophytum comosum), a frequent houseplant, seeks the airy spaces around it to grow an appendage at the end of which will be flowers or a new sapling, thus allowing a greater degree of exposure to the first and reducing competition with the suckers by putting soil half.

Examples of negative tropism

1. Negative phototropism. Some aquatic plants grow in the opposite direction to the constant presence of sunlight, or at least to its direct incidence, since this would sooner or later lead to the evaporation of the water and therefore it would harm it. Thus, the plant grows in the opposite direction, fleeing the sun towards more humid areas.
2. Negative geotropism. Just as the roots go in favor of gravity, the stems of the plants always go against it and in this they show negative geotropism. This is because when germinating usually underground, the stems will need to emerge to the surface in order to later expose the leaves to the air and receive sunlight. If they grew as roots, they would never find an iota of light.
3. Negative thigmotropism. Commonly, non-climbing or non-creeping plants will respond to the constant presence of a good-sized object in their growing zone by varying the route of its stems and trying to escape into the open air, especially if the object in question restricts sunlight, water or the space of increase. This can be seen in trees planted very close to buildings.
4. Negative hydrotropism. Since excess water can be as lethal to plants as its absolute scarcity, many plants germinate on the margins of lakes and rivers and grow towards the dry, since it offers them better possibilities of survival. It is a case of negative hydrotropism, although these plants will continue to need water to live.
5. Negative aerotropism. In eventual conditions of earth movements or other types of eventualities that would expose the roots of a tree, they they will avoid the air and will seek to re-enter the earth, at any cost, since they will not be able to extract their nutrients from the air.