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 



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

 organ that bears it. A root differs of the Indian com; a, root 

 ,. 111 1-1 cap; b, embryonic region; 



from a branch also, as a rule, in the 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 



FIG. 104. Lengthwise 



