44 ELEMENTARY BIOLOGY 



the toughness and rigidity of the cyhnder. Bundles of fibers 

 with water-conducting vessels or of fibers with food-conducting 

 vessels are called fibro-vasadar bundles, the term fibro mean- 

 ing " of fibers " and vasailar meaning " of vessels," or tubes. 



68. Growth of roots. The fiber and vessel cells are capable 

 of growth, but they are not capable of cell division. In the 

 young root there appear layers of cells which separate the water- 

 carrying bundles from the food-carrying bundles. These canibimn 

 cells are capable of producing new fiber and duct cells of the two 

 kinds — the water-carrying, or wood, and the food-carrying, or 

 bast, systems (see pp. 174-177). Growth in length results from 

 the formation of new cells by a special growing layer near the 

 tip of the root. 



69. Forms of roots. The structure of roots is fairly uniform 

 for different kinds of plants. But roots nevertheless appear 

 in very many different forms, from the thin, stringy roots of 

 grains to the massive fleshy or woody roots of beets or trees. 

 These differences are found to be closely related, in many 

 cases, to the conditions under which the plants live. Thus, 

 fleshy roots are often associated with the biennial habit. In 

 such plants as beets, carrots, and parsnips the first season of 

 the plant's growth i? spent in manufacturing food and deposit- 

 ing it in the root. The next year comparatively little foliage 

 is produced, but a stalk bearing flowers (which in turn develop 

 into fruit, bearing seeds) uses up practically all the food that 

 has been left over from the previous season. In contrast with 

 this habit of life we find the plants that sprout, grow up into 

 maturity, and die, all within one season. These annual plants 

 have, as a rule, rather delicate, or fibrous, roots. 



Trees and woody shrubs, which continue to live year after 

 year, develop massive shoots. Corresponding to this fact we 

 may note that such plants also develop elaborate, strong roots. 

 From this we may see that the structure of the root and its 

 functions are closely related to each other and to the character 

 of the plant. There is a connection, on the one hand, between 



