28 THE NATURE AND WORK OF PLANTS 



trated trees. The side roots contract in the same 

 manner so that the entire root system is a great com- 

 plex clamp which grasps the soil and rocks very 

 firmly, and thus greatly increases the anchoring 

 power of the underground organs. 



27. 2'he structure of the root. — Examine an old 

 root that has begun to decay. Material from a 

 hyacinth or calla will be suitable. Hold the large 

 end in one hand and strip off the outer delicate tis- 

 sue, when a central cord or fibrous mass will be seen. 

 When the organ is growing rapidly the outer cylin- 

 der of soft tissue absorbs water and expands, stretch- 

 ing the central fibrous cord as one might a rubber 

 string. When the root grows old the outer tissues 

 change their form, allowing the central cord to 

 shorten, and wrinkling the epidermis in the process. 



28. Clinibing roots. — A large number of species 

 of the higher plants form long slender stems which 

 are unable to stand upright, and which are specially 

 adapted for attachment to the trunks of trees and 

 other tall objects, to which they are fastened by 

 various methods. In many instances roots are de- 

 veloped many feet above the ground, and these 

 adhere to the tree in various ways, holding the stem 



