GENEEAL MOEPHOLOGY OP THE PLANT 19 



ment each branch normally arises nearer to the apex than the 

 one before it, so that the youngest is always the nearest to the 

 tip. This mode of origin is known as acropetal succession. 

 It is not confined to roots, but is a feature of branching in 

 general. 



Oooasionally, however, roots arise at other places than 

 their normal point of origin. Such are known as adventitious 

 roots. Examples may be seen in the roots produced upon the 

 stems of the Ivy and other plants, by which they are enabled to 

 attach themselves to the surfaces over which they are climbing. 

 Very frequently roots of this description are developed from 



Fig. 21. 



Fi'j. 21. The Banyau-tree (7^ic«s i/i'/im). 



injured surfaces, as in the case of those plants which are pro- 

 pagated by means of cuttings. AVhen a young twig of a Geranium 

 is severed from the stem and its cut end embedded in moist soil, 

 it shortly puts out these adventitious roots from the out surface 

 and develops into a new Geranium plant. Adventitious roots 

 can also be made to arise from leaves, as in the case of some 

 species of 'Begonia and of Bryophyllum. In many other 

 plants aerial roots belonging to this class are given off by the 

 stem or branches, which descend to the ground, and, fixing them- 

 selves there, not only act as mechanical supports, but assist the 

 true root in obtaining food. Such roots are well seen in the Banyan 

 or Indian Fig-tree (fig. 21), and in the Mangrove (fig. 22). 



