PART I.-MORPHOLOGY. 



CHAPTER I. THE EOOT. 



6. The first root developed by Primary, 



a seedling is called the primary root. All other roots Secondary 

 whether developed from the primary root, or from other Adventitious 

 parts of the plant, are called secondary. The root, like the Roots. . ^ 

 shoot, is capable of branching and rebranching, the new 

 roots being normally developed in longitudinal rows, laterally, 

 on the parent root, in such a way that the youngest are always 

 nearest the growing-apex of the mother-root, i.e. they are 

 developed in acropetal succession and a line, following the 

 course of development of the lateral roots, passes from the 

 oldest ones at the base of the parent-root to the youngest ones 

 at its apex. 



The young roots are developed from the inner tissues of 

 the parent-root and as they grow they break through the outer 

 tissues. This can be well seen in the long roots which hang 

 from the branches of the Banyan (Ficus bengalensis), the 

 young roots pushing through cracks in the outer tissues of the 

 parent roots. The aggregate of roots developed by a plant 

 constitutes its root-system. All roots which are not branches of 

 the primary root, or which, being such branches, are not 

 developed in acropetal succession, are said to be adv entitious, 

 this term being applied to all parts of plants which develop 

 either in abnormal positions, or out of their proper order. 

 Roots, therefore, may first of all be classified according to their 

 mode of origin into : 



(1) Primary. 



(2) Secondary ] }?> t V 



J {(0) Adventitious. 



Roots which spring from the stem are therefore adventi- 

 tious, such as are those often seen on the sugarcane as shown 

 in Plate I, Fig. 4. 



7. If we examine the seedling Types O f 



of one of our common forest trees, say an Oak. we shall Root- 

 find that the primary root elongates and continues to yst< IM 

 grow vigorously for a considerable period. Such a root is 

 termed a tap-root and all the roots developed from it are its 

 lateral roots, see Fig. 7, Plate I. If the tap-root is injured a 



