WORK OF THE ROOT 



45 



is performed. Some of this energy appears as heat which 

 helps to maintain a suitable temperature within the living 

 tissues of the plant. 



In describing the Stock we spoke of the growing-points 

 of root and stem. The root in pushing its way through the 

 soil meets with much resistance, but is protected at the 

 tip by a root-cap, the end of which is constantly dying 

 and wearing away, to be re- 

 placed by new tissue. On the 

 other hand, the stem-tip has no 

 cap, but is protected by the 

 overlapping leaves which form 

 the end bud. 



Growing-region of the root. It 

 will be interesting to compare 

 the manner of growth of root 

 and stem and to determine 

 experimentally the mode of 

 elongation in each case. 



Select a germinating Bean 

 with a radicle about an inch 

 long, wipe off adhering par- 

 ticles, taking care not to injure 

 the Bean in any way, and 

 mark about a dozen lines across 

 it in Indian ink. This can be 



done as follows: Take a piece of cotton thread and 

 hold it by both ends ; bend it, and dip the middle of 

 the thread into the ink. Then lay it across the root 

 so as to make a clear transverse mark. Begin quite 

 at the tip and make a series of marks about * inch 

 apart backwards from the tip. Obtain a large, wide- 

 mouthed bottle or jar fitted with a cork (Fig. 21). 

 Line it with blotting paper so that the lower edge dips 

 into about half an inch of water ; this provides a moist 



Fig. 21. Bean Seedling 

 marked to determine the 

 Region of Elongation in 

 the Root. 1, at the com- 

 mencement of the experi- 

 ment; 2, at the end of 3o| 

 hours. 



