PLANT STEMS 227 



6. 1402 : 64-73. How the Plant Takes in the Soil Water. 



c. 1404 : 87-162. The Work of Roots. 



d. 1405:31-44. Roots. 



e. 1406 : 120-125. Function and Structure of Roots. 

 /. 1603 : 27-40. The Soil and the Water. 



g. 1604:124-138. Roots. 



h. 1902:98-101. Root-tubercle Bacteria. 



Experiment 76. Effect of Plant Roots on Soil. 



Apparatus: Saucer, cloth. 



Materials: Radish seeds, litmus paper (blue), blotting 

 paper, distilled water. 



a. Place a piece of blue litmus paper upon the saucer, and 

 on it place several radish seeds. Cover the seeds with an- 

 other piece of blue litmus paper, and place over the latter a 

 piece of blotting paper. Moisten all of the paper with dis- 

 tilled water, and cover with a dry cloth. Moisten each day, 

 if necessary, and note any change in the litmus paper. What 

 are your conclusions ? 



164. PLANT STEMS 



The purpose of the stem is to hold up the leaves and flowers 

 to the light, and to supply them with the materials for plant 

 food. Some stems also store food, after it has been made 

 by the leaves, while the stems of a few plants aid in the mak- 

 ing of the food. The propagation of some plants is produced 

 by their stems. The main stems, since strength is required, 

 tend to become woody, and in trees serve as a source of wood. 



Stems are composed of bundles of very fine tubes through 

 which the sap rises, partly on account of capillarity (see 

 Section 118), and partly due to the osmotic pressure of the 

 roots. See Section 119, Osmosis. The complete explana- 

 tion of the movement of sap is not known. 



