3H 



ZONES AND REGIONS 



[Pt. Ill, Skct. I 



directl}^ against the support ; they grow nearly horizontally, whether it be 

 owing to diagcotropism or to rectipetality. In the histological structure 

 of the anchoring-roots the mechanical elements are prominent, particularly 

 in the form of tough fibres, whilst the conducting elements are very poorly | 

 developed (Fig. 155,/'). 



The ahsorbiiig-roots are markedly positively geotropic and grow down- 



FiG. 154. Stem of Philodendion melano- 

 chrysuin uith vertical absorbing-roots and 

 horizontal anchoring-roots. One-sixth natural 

 size. Alter Went. 



KiG. 155. Aiithiirium sp., from Trinidad. 

 Epiphytic liane. Transverse sections of roots. 

 a absorbing-root ; /' anchoring-root. Mag- 

 nified 10. 



wards without branching until they reach the ground ; once there, apical 

 growth usually ceases soon, while numerous lateral roots spring from the 

 apical region and descend vertically into the soil.' The same thing happens 

 if the roots reach water. In many species, the absorbing-roots creep over 

 the surface of the bark, alongside of their own stem ; but in others, 

 particularly in those that climb high up among the branches, the absorbing- 

 roots descend freely through the air, and, after emitting terrestrial roots. 



