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Plants can respond to both stimuli directional and non directional. The directional response to a stimulus such as gravity or sunlight , is called tropism and a non-directional response to a motion nástico .
Tropisms are the result of differentiated cell growths in which cells of a plant part are elongated more than the other, causing it to tilt towards the side with lower growth. Among the most common tropism is the phototropic , the inclination of the floor toward a light source. Phototropism allows you to maximize light exposure in those requiring additional light for photosynthesis or minimize where they are subject to intense light and heat. The geotropism allows the roots to determine the gravity and grow downwards. Tropisms are generally the result of the interaction between the medium and production of one or more plant hormones.
Unlike tropisms, the nastic movements result from changes in osmotic pressure within plant tissues, and can occur quickly. A familiar example is the seismonastia (response to touch or vibration) in the Venus flytrap , a carnivorous plant. The traps consist of modified leaves shovel shaped sensitive hairs located inside of the sheet. When an insect or other animal touches these hairs the sheet is folded. Although the trap is closed quickly due to pressure changes produced in the cells, it must reopen slowly to allow time for digesting plant food.

Economically, one of the most important areas of research in ecophysiology is the pathology , the study of diseases and how they resist or cope with the infection. Plants are susceptible to the same animal pathogenic organisms, including bacteria , viruses and fungi , as well as physical invasion of insects and nematodes .
Since plant biology differs from the animal, its symptoms and responses are also different. In some cases, a plant can simply dispose of their leaves or flowers to avoid spreading the disease, in a process called abscission . Plants, unlike the animals, which can spread a disease by casual physical contact, tend to disseminate pathogens through spores or are carried by vectors animals.
One of the most important advances in the control of plant diseases was the discovery in the nineteenth century, the Bordeaux mixture . This broth, comprising copper sulfate and calcium oxide (quicklime), is the first fungicide known. His application was used to inhibit the growth of mildew that threatened the French wine industry seriously.

Sir Francis Bacon published one of the first experiments on plant physiology in 1627, in the book Sylvarum Sylva . Bacon grew several terrestrial species, including a rose in water and concluded that only the substrate is needed to keep the plants upright. Jan Baptist van Helmont published what is considered the first quantitative experiment in this area in 1648. For five years, cultivated a willow in a pot containing 90.718 kg of substrate dried in an oven. This substrate lost only 900 grams of weight and van Helmont concluded that plants get all their weight of water, not soil.
In 1699, John Woodward published experiments on growth of spearmint in different water types and found that growing much better in water with added substrate instead of distilled water.
A Stephen Hales is considered the father of plant physiology because of the many experiments and collected in the book 1727, 5 although Julius von Sachs unified the different parts of plant physiology as a discipline combining them. His Lehrbuch der Botanik was like the bible of the field in their time. 6
During the 1800s, researchers discovered that plants absorb essential mineral nutrients as inorganic ions from water. Under natural conditions, soil acts as a storehouse of mineral nutrients, but the soil itself is not essential for growth. When the mineral substrate is dissolved in water the roots of the plant are absorbed rapidly, the soil is no longer needed for this thrive. This observation is the basis of hydroponics , growth in a liquid solution rather than substrate, which has become a standard technique in biological research, educational exercises in laboratories or production of crops as a hobby.





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