The New Student's Reference Work/Nutrition

Nutri′tion (in plants), the processes by which food is obtained and utilized.  Plants obtain their food (which see) in two ways, by absorption and by manufacture.  With a few exceptions, plants which obtain their food ready-made are unable to engulf it and must take it into the body in solution.  (See Absorption.)  If insoluble in water, they must first digest it.  (See Digestion.)  All prepared food is derived directly or indirectly from other organisms.  A few plants capture small insects for the sake of the food derived from their bodies.  Parasites, that is, creatures growing on or in a living being (called, therefore, the host), derive their food directly from it; saprophytes in a similar way obtain their food from a dead organism.  There is every possible gradation between parasites and saprophytes; and between saprophytes and green plants, which are able to make all of their food out of inorganic material.  Yet many green plants absorb organic matter, i. e., matter once a part of a living being; this is the reason for applying fertilizers and manures to gardens and fields.  Many, perhaps all, colorless plants can make the most complex foods (proteids), provided simpler foods and necessary salts are supplied.  Only green plants, however, and of these only the green parts, can make carbohydrate foods, like sugars, starch and the like, out of carbon dioxide and water.  (See Photosynthesis.)  When these foods have been formed in sufficient amount, the green plants can also produce proteids.  Most plants make more food than they require.  Reserve food is stored, usually in solid form, in special tissues.  These storage regions have been greatly improved by cultivation, the common vegetables (seeds, tubers, bulbs, roots, leaves, and even flower buds) being the product of proper breeding and of growing the plants under unusually favorable conditions for nutrition.  In its broadest sense, nutrition includes the use of foods in assimilation, respiration and growth.  These topics are separately treated.  In the course of the chemical processes of nutrition (see Metabolism) a great variety of waste products arise, such as gums, resins, volatile oils, tannins, alkaloids etc.  These the plant secretes and removes them thus from its general metabolism.  See Secretion.