Plant Structure, Function, and Use

Plant Responses to Stimuli

What is symbiosis?

The term “hydroponics” refers to growing plants in some medium other than soil—usually a liquid solution, with the inorganic plant nutrients (such as potassium, sulfur, magnesium, and nitrogen) continuously supplied to the plants by the solution. It was first pioneered by Julius von Sachs (1832–1897), a researcher in plant nutrition; in 1937, William Frederick Gericke, a scientist at the University of California, defined the word hydroponics (although he asserted that the term was actually suggested by W. A. Setchell of the University of California)— and he proved its worth by growing twenty-five-foot tomato vines in his backyard using hydroponics.

Now hydroponics is mostly used in areas where little or unsuitable soil is available or poor weather conditions, such as growing vegetables in the Middle East or in Antarctica. In addition, because it calls for precise control of nutrient levels and oxygenation of the roots, it is often used to grow plants for research or commercial uses. And although successful for research, hydroponics has many limitations—which is why the average gardener who tries to grow plants hydroponically should have a great deal of patience!

Symbiosis is the close association of two or more different organisms. One type of symbiosis is known as mutualism, defined as an association that is advantageous to both parties. The most common (and possibly the most important) mutualistic, symbiotic relationship in the plant kingdom is known as mycorrhiza—a specialized association between the roots of plants and fungi that occurs in the vast majority of both wild and cultivated plants. (For more about symbiosis in animals, see the chapter “Aquatic and Land Animal Diversity”; for more about mycorrhiza, see the chapter “Fungi.”)


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