HOW PLANTS OBTAIN THEIR LIQUID FOOD. 39 



the root hairs have a cell-sap which is now more concentrated 

 than the diluted cell-sap of the hairs, and consequently gain some 

 of the food solutions from the latter, which tends to lessen the 

 content of the root hairs and also to increase the concentration of 

 the cell-sap of the same. This makes it possible for the root hairs 

 to draw on the soil for more of the food solutions, and thus, by 

 a variation in the concentration of the substances in solution in 

 the cell-sap of the different cells, the food solutions are carried 

 along until they reach the vascular bundles, through which the 

 solutions are carried to distant parts of the plant. In this way a 

 pressure is produced which causes the liquid to rise in the plant. 

 77. How the root hairs get the watery solutions from the 

 soil. — If we examine the root hairs of a number of seedlings 

 which are growing in the soil under normal conditions, we shall 



Fig. 25. 

 Root hairs of corn seedling with soil particles adhering closely. 



see that a large quantity of soil readily clings to 

 the roots. We should note also that unless the 

 soil has been recently watered there is no free water in it; the 

 soil is only moist. We are curious to know how plants can 

 obtain water from soil which is not wet. If we attempt to 

 wash off the soil from the roots, being careful not to break 



