THE ROOT 



225 



trees are anchored in the ground bj side-roots can be seen in 



the large buttresses at the bases of some of them. If these are 



cut or sawn^ across, it will appear that their shape is almost like 



planks set edgewise. "The astonishing strength of tree-roots can 



be imagined when we watch a tree in full leaf during a storm. 



As the terrific force of the gale sways the trunk to and fro, the 



roots are subjected to an enormous pull. Like great India 



rubber cables they give and retract, and when the wind subsides, 



we find the trunk as firm as ever." 



(c) In which part the growth of the root takes place can be 



experimentally seen in the 



following way: we take a few 



germinating seeds of the Bean 



and mark the root from its tip 



with Indian ink at intervals of 



exactly one-eighth of an inch. 



Then we pin the seed to the 



lower side of a cork fitting into 



a wide-necked flask. To afford 



the seed the required moisture 



there should be a little water 



in the flask. After twenty-four 



hours we find the root to have 



grown considerably, and from the distances of the marks we 

 distinctly gather that growth took place only at a 

 short stretch above the root-end. The tip of the root 

 is, so to say, forced into the soil. 



(d) The root-tip is, however, exceedingly tender, 

 and when it is forced into the soil so energetically, 

 the tip must be protected from injury. Examine, with 

 a hand-lens, the root-tip of a Tradescantia grown in 

 water, or of a germinating Sunflower. You will find 

 that it is covered over by a protective cap, the 7'oot- 

 cap. It consists of a cellular tissue, which is constantly 

 renewed from within to replace the old cells which 

 get worn out and swell up jelly-like, giving the tip 



a slippery touch, as can be noticed in the pendulous aerial 



Fig. 208. — Growth of i*oot taking place 

 behind the root-end. 



^ 



Fig. 209.— 

 Root-cap of 

 Pandanus. 



15 



