CHAPTER XV 



CLASSIFICATION OF ROOTS AND STEMS 

 CLASSIFICATION OF ROOTS 



Roots may be classified as to their duration, their order in time of 

 development, place or nature of origin, function, form, and consistency. 



Duration of Roots. — As to duration, we have roots divided into two 

 great classes, although the terms designating them are in general applied 

 to the plant as a whole rather than to the root. Monocarpous plants 

 are those which die after producing one crop of fruit; Polycarpous, 

 those which produce successive crops. The former are Annual when 

 they live but a single season — as the rag- weed and the sunflower; 

 Biennial, when they devote the first season to the storing up in some 

 receptacle, such as a fleshy root or bud, a supply of nutriment, and 

 fruit and die in the second season. The term winter-annuals has been 

 applied to those which begin their life during the latter part of the first 

 season, fruiting early the next season, so that their combined life during 

 the two seasons is less than twelve months, as in the case of wheat and 

 rye. Such may, by being planted early in the season, finish their 

 existence during one season, as in the case of spring wheat. Those 

 monocarpous roots which devote a number of years to the preparation 

 for fruiting, as in case of the century plant, belong to the Perennials. • 

 All Polycarpous roots belong, of course, to the perennials. 



Order of Development. — Primary and Secondary Roots. — As to their 

 order in time of development, the first root developing from the radical 

 is the primary. All subsequently developed, whether from root or 

 stem, are secondary, although those developing from secondary roots 

 are sometimes designated Tertiary and so on. 



The Tap Root. — If the primary root continue its development so as 

 to constitute a branch-bearing axis, it is called a Main-root or Tap-root 

 (F'ig. 439). The ultimate behavior of the tap-root, when not of the 

 fleshy- thickened storage class, depends upon the development of the 

 leafy crown of the stem. The extent of root-growth and its development 

 will agree with that of the stem-crown. Two forms of stem-crown are 



