CHAPTER XIV 



ROOTS AND THEIR USES 



192. Origin and Growth of Roots. — A root may originate 

 in any one of three different ways : as a primary root, which 

 develops from the radicle of the embryo and is continuous 

 with the stem of the plant ; as a 

 branch root, growing out from the 

 primary root or from an older branch 

 root ; or as an adventive root, starting 

 from some part of the plant other 

 than a root — usually from the stem 

 or from a branch. A branch root or 

 an adventive root nearly always be- 

 gins its growth deep within the 

 tissues of the organ (root, stem, or 

 branch) from which it starts. This 

 is one way in which a root usually 



differs from a branch, which begins ^^^ 104, - Lengthwise 

 as a swelling upon the surface of the section through a root tip 



A root differs °^ '^^ Indian com ; a, root 

 cap; b, embryonic region; 

 c, region of growth, 

 arrangement of its tissues, in having 



its growing point protected by a root-cap, and in not bear- 

 ing leaves. However, it is sometimes difficult to say 

 whether a particular structure is a root or a branch, just 

 as at other times we cannot be sure whether a certain 

 organ is a branch or a leaf. So we must think of stems, 

 branches, leaves, and roots as classes into which it is con- 

 venient to divide the organs of plants ; but these classes 



169 



organ that bears it. 



from a branch also, as a rule, in the 



