Plants have no feet and they cannot simply move from one place to another when things get tough. So, in order to survive, plants have developed complex sensory and regulatory systems which enable them to constantly adapt to changes and challenges in their environment.
The different parts of a plant are closely interconnected, so that roots, leaves, flowers, and stems can easily exchange vital information. This network enables plants to distinguish between different types of light and to respond accordingly. They can distinguish smells around them and can activate defence mechanisms according to what they perceive from their surrounding environment. Plants know when they are being touched and can distinguish between different types of touch. They are also aware of gravity, which allows them to grow shoots upwards and roots downwards. Plants also have a memory, and can remember past infections and modify their physiology based on these memories.
A Douglas fir, for example, a common plant in the coastal regions of North America, needs to know how strong the northerly winds are, so that it can grow a trunk that is solid enough to withstand these forces and survive in an environment where more fragile plants would be flattened in one gust. Similarly, an elm tree cannot grow unless it finds a way to take full advantage of the light available in its immediate surroundings, especially if all the neighbouring trees are taller. Vegetables, on the other hand, must be able to sense the presence of aphids so that they can defend themselves against an attack.
