STRUCTURE AND WORK OF PLANTS 9 



network in the region about the tip of the rootlet. If the 

 seedlings are grown in sawdust, on damp blotting paper, or 

 within earthen pots that are kept moist by covering or by 

 being inverted upon a damp surface, they will afford interest- 

 ing demonstrations of how rootlets and root hairs grow under 

 different conditions. 



9. Roots and their work : water-lifting power. If the top 

 of a vigorously growing potted plant is cut off and an upright 

 glass tube is attached to the plant stump by means of a rubber 

 tube, water may be forced upward in the latter, thus showing 

 that roots can lift water from the soil. Actively growing trees 

 and shrubs, when cut, often show this same phenomenon by 

 forcing out through the cut surface some of the water that 

 is brought up from the soil. This is sometimes incorrectly 

 spoken of as " bleeding " of the stump. The roots, however, 

 are not the only parts of the plant that may lift water. That 

 the leaves and stem may also do this work may be shown by 

 cutting off the top of a plant under water, and, while still under 

 water, attaching the stem to a water-filled U-shaped tube. The 

 top of a plant that has been so treated may continue to lift 

 water for several days. 



In plants that are growing normally, the roots, by means of 

 the root hairs, take up water from the soil. It passes into the 

 interior of the rootlet, then into the larger roots, into the stem, 

 and finally into the leaves. Some of this water is carried from 

 the leaves into the air, and that process will be discussed under 

 the topic transpiration. 



10. Roots and their work : turgidity. Eoot hairs and other 

 cells of plants usually take up water until the cell walls are 

 distended with water and protoplasm. The outward pressure 

 which distends and stretches the walls is called turgor, and the 

 resulting condition is called twrgidity. Turgor doubtless helps 

 to force water upward through the stem. The distention of 

 cells due to turgor also accounts for the rigid or erect position 

 of most leaves, growing shoots, and succulent stems. Each 

 distended cell, like an inflated balloon, assumes a semi-rigid 



