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TEXTBOOK OF BOTANY 



Fig. 221. Two parasitic plants of Louisiana broom-rape (Orobanche) attached by 

 haustoria to roots of a tobacco plant. Photo by A. L. Pierstorff. 



Non-green plants live in all sorts of habitats in water and soil, and also 

 within and on the bodies of plants and animals. Those that grow within 

 or on the living tissues of plants and animals and obtain food from them 

 are parasites. Those that obtain food from the dead bodies of plants and 

 animals, from their products, or from their non-living parts, such as the 

 dead bark and heartwood of trees, are saprophytes. If thev can grow onlv 

 within living tissues they are called obligate parasites. If they cannot 

 grow within living tissues, they are said to be obligate saprophytes. But 

 if they can grow either as parasites or as saprophytes, they are referred 

 to as facultative species. There are all sorts of gradations between sapro- 

 phytic and parasitic plants. 



With the exception of a few special groups of bacteria, non-green 

 plants cannot svnthesize sugar. Some of them, such as veast, when sup- 

 plied with an external source of sugar, inorganic salts, and water, can 

 make the rest of the foods necessary for growth and reproduction. 

 Others are dependent upon an external source of amino acids, or of pro- 

 teins also. Plants that can svnthesize su2;ar are sometimes called auto- 

 phytes in contrast to parasites and saprophvtes. In addition to food, non- 

 green plants may also be dependent upon an external supply of certain 

 vitamins and hormones. 



