PLANT EOOTS 



187 



cell solution does move out, however, and it is this which 

 helps to dissolve the soil particles. The protoplasm in the 

 cell regulates to some extent the interchange of liquids. 



Experiment 93. Cut off the stem of a thrifty geranium, begonia, 

 or other plant an inch or two above the soil. Join the plant stem by 

 a rubber tube to a glass tube a meter long, of about the same diame- 

 ter as the stem. See that the rubber tube clings strongly 

 to both glass tube and stem. It may be best to tie it 

 tightly to these. Support the glass tube in a vertical posi- 

 tion above the stem and pour into it sufficient water to rise 

 above the rubber tube. Note the position of the water 

 column. "Thoroughly water the soil about the plant. 

 Watch the height of the water column, marking it every 

 few hours. 



The water taken in by the roots passes on from 

 cell to cell by osmotic action and rises in the stem 

 in the same way that the water rose in the tube 

 attached to the stem of the growing plant in Experiment 

 93. The root pressure, together with capillarity, as seen 



in Experiment 54, will 

 account for the rise of 

 the sap in lowly plants, 

 but the cause of the rise 

 of the sap to the top of 

 lofty trees is difficult to 

 understand. 



Roots extend them- 

 selves through the soil 

 by growing at the tips. 

 Fi S- 86< Here the cells are rapidly 



dividing, forming new cells and building root tissue. As 

 water is so essential, they are always seeking it and ex- 

 tending themselves in the direction where it is to be found. 

 This causes them to extend broadly and to sink deeply 

 (Fig. 86). A single oat plant has been found to have an 



